Glossary of Neurosurgical Terminology


ABSCESS– A circumscribed collection of pus.

ACOUSTIC NEUROMAS – Benign tumor of the hearing nerve (eighth nerve).

ACROMEGALY – Disorder marked by progressive enlargement of the head, face, hands, feet and thorax, due to the excessive secretion of growth hormone.

ADENOMA – A benign growth formed of glandular tissue.

AGNOSIA – Absence of the ability to recognize the form and nature of persons and things.

AGRAPHIA – Inability to write due either to muscular coordination issues or to an inability to phrase thought.

AMAUROSIS– Loss of vision without a visible lesion in the eye structures or optic nerve.

AMAUROSIS FUGAX – Temporary blindness occurring in short periods.

AMENORRHEA – Absence of the menses due to causes other than pregnancy or age.

AMNESIA – Loss of memory caused by brain damage or by severe emotional trauma.

ANALGESIA – Loss of sensitivity to pain, loss of response to a painful stimulus.

ANAPLASIA – In the case of a body cell, a reversion to a more primitive condition. A term used to denote the alteration in cell character that constitutes malignancy.

ANASTOMOSIS – A communication, direct or indirect: a joining together. In the nervous system a joining of nerves or blood vessels.

ANESTHESIOLOGIST – Physician who administers pain-killing medications during surgery.

ANENCEPHALY – Absence of the greater part of the brain, often with skull deformity.

ANESTHESIA – Loss of sensation of a body part or of the body induced by the administration of a drug.

ANESTHESIOLOGIST – Physician who administers pain-killing medications and monitors complications and reactions during surgery.

ANEURYSM – Dilation of an artery, formed by a circumscribed enlargement of its wall.

ANGIOGRAM – A medical imaging report that shows the blood vessels leading to and in the brain, obtained by injecting a dye or contrast substance through a catheter.

ANGIOGRAPHY – Radiography of blood vessels using the injection of material opaque to X-rays to give better definition to the vessels.

ANOREXIA – An eating disorder marked by loss of appetite leading to excessive weight loss.

ANOSMIC – Without the sense of smell.

ANOXIA – An absence of oxygen.

ANTI-COAGULANT – A medication that prevents coagulation (clotting) of the blood.

ANTIDIURETIC – An agent that reduces the output of urine.

APHASIA – Difficulty with or loss of use of language in any of several ways, including reading, writing or speaking, not related to intelligence but to specific lesions in the brain.

APNEA – Temporary cessation of breathing.

APOPLEXY – Often used as equivalent to stroke, this is a condition in which there is bleeding into an organ or blood flow to an organ has ceased.

ARACHNOID – Middle layer of membranes covering the brain and spinal cord.

ARACHNOIDITIS – Inflammation of the arachnoid membrane, most commonly seen around the spinal cord and cauda equina.

AREA – (Cortical) – A part of the brain having a special function as in

  • Motor – The cortical portion of the brain controlling movement.
  • Sensory – The cortical portion controlling sensation.

ARTERIOGRAPHY – See angiography.

ARTERIOSCLEROSIS – Thickening and calcification of the arterial wall with loss of elasticity and contractility.

ARTERIOVENOUS – Relating to both arteries and veins.

ARTERIOVENOUS MALFORMATION – Collection of blood vessels with one or several abnormal connections between arteries and veins, which may cause hemorrhage or seizures.

ASTROCYTE – Cell that supports the nerve cells (neurons) of the brain and spinal cord.

ASTROCYTOMA – Tumor within the substance of the brain or spinal cord made up of astrocytes; often classified from Grade I (slow growing) to Grade III (rapid growing).

ATAXIA – A loss of muscular coordination, abnormal clumsiness.

ATHETOSIS – A condition in which there is a succession of slow, writhing, involuntary movements of the fingers and hands, and sometimes of the toes and feet.

ATROPHY – A wasting of the tissues of a body part.

AUTONOMIC NERVOUS SYSTEM – Involuntary nervous system, also termed the vegetative nervous system. A system of nerve cells whose activities are beyond voluntary control.

AVASCULAR – Non-vascular, not provided with blood vessels.

AXON – The part of a nerve cell that usually sends signals to other nerves or structures.


BACTERICIDAL – Causing the death of bacteria.

BACTERIOSTATIC – Inhibiting or retarding the growth of bacteria.

BELL’S PALSY – Paralysis of facial muscles (usually one side) due to facial nerve dysfunction of unknown cause.

BIOPSY – Removal of a small portion of tissue, usually for making a diagnosis.

BLOOD-BRAIN BARRIER – The barrier that exists between the blood and the cerebrospinal fluid, which prevents the passage of various substances from the bloodstream to the brain.

BRADYCARDIA – Slowness of the heart rate.

BRADYKINESIA – Slowness in movement.

BROWN-SEQUARD’S SYNDROME – Loss of sensation of touch, position sense and movement on the side of a spinal cord lesion, with loss of pain sensation on the other side. Caused by a lesion limited to one side of spinal cord.


CARCINOMA – Cancer, a malignant growth of epithelial or gland cells.

CAROTID ARTERY – Large artery on either side of the neck that supplies most of the cerebral hemisphere.

CAROTID SINUS – Slight dilatation on the common carotid artery at its bifurcation containing nerve cells sensitive to blood pressure. Stimulation can cause slowing of the heart, vasodilatation and a fall in blood pressure.

CARPAL TUNNEL – Space under a ligament in wrist through which the median nerve enters the palm of the hand.

CT SCAN – (computed tomography scan) A diagnostic imaging technique in which a computer reads X-rays to create a three-dimensional map of soft tissue or bone.

CATHETER – A small tube used to inject a dye to see the blood vessels, similar to that used for looking at vessels in the heart. May also be used to facilitate drainage.

CAUDA EQUINA – The bundle of spinal nerve roots arising from the end of the spinal cord and filling the lower part of the spinal canal.

CAUDATE NUCLEUS – Part of the basal ganglia, which are brain cells that lie deep in the brain.

CEREBELLUM – The lower part of the brain that is beneath the posterior portion of the cerebrum. It regulates unconscious coordination of movement.

CEREBROSPINAL FLUID – Water-like fluid that circulates around and protects the brain and spinal cord.

CEREBRUM – The principal portion of the brain, which occupies the major portion of the interior of the skull and controls conscious movement, sensation and thought.

CERVICAL – Of or relating to the neck.

CHIASM (OPTIC)– Crossing of visual fibers as they head toward the opposite side of the brain. For each optic nerve most of the visual fibers cross to the opposite side, while some run directly backward on each side without crossing.

CHOREA – A disorder, usually of childhood, characterized by irregular, spasmodic involuntary movements of the limbs or facial muscles.

CHOROID PLEXUS – A vascular structure in the ventricles of the brain that produces cerebrospinal fluid.

COCCYX – The small bone at the end of the spinal column , formed by the fusion of four rudimentary vertebrae. The “tail bone”.

COMA – A state of profound unconsciousness from which one cannot be roused.

COMPUTED TOMOGRAPHY (CT) SCAN – A diagnostic imaging technique in which a computer reads X-rays to create a three-dimensional map of soft tissue or bone.

CONCUSSION – A disruption, usually temporary, of neurological function resulting from a blow or violent shaking.

CONTRAST MEDIUM – Any material (usually opaque to X-rays) employed to delineate or define a structure during a radiologic procedure.

CONTUSION – A bruise; cerebral contusions often involve blood vessels that leak into brain tissue.

CORONAL SUTURE – The line of junction of the frontal bones and the parietal bones of the skull.

CORTEX – The external layer of gray matter covering the hemispheres of the cerebrum and cerebellum.

CRANIUM – The part of the skull that holds the brain.

CRANIECTOMY – Excision of a portion of the skull.

CRANIOPHARYNGIOMA – Tumor arising from the embryonic duct between the brain and pharynx.

CRANIOPLASTY – The operative repair of a defect of the skull.

CRANIOSYNOSTOSIS – Premature closure of cranial sutures, limiting or distorting the growth of the skull.

CRANIOTOMY – Opening of the skull, usually by creating a flap of bone.

CSF – Cerebrospinal Fluid.


DEPRESSED SKULL FRACTURE– A break in the bones of the head in which some bone is pushed inward, possibly pushing on or cutting into the brain.

DIABETES INSIPIDUS – Excretion of large amounts of urine of low specific gravity. The inability to concentrate urine.

DIFFUSE AXONAL INJURY – Damage to the axons of many nerve cells that lie in different parts of the brain.

DIFFUSE BRAIN INJURY – Damage to the brain that can affect many parts of the brain, often in a subtle fashion; examples include diffuse axonal injury and inadequate blood flow.

DIPHENYLHYDANTOIN – Dilantin; a medication used to control seizures.

DIPLOPIA – Double vision, due usually to weakness or paralysis of one or more of the extra-ocular muscles.

DISC – The intervertebral disc – cartilaginous cushion found between the vertebrae of the spinal column. It may bulge beyond the vertebral body and compress the nearby nerve root, causing pain. The terms “slipped disc”, “ruptured disc” and “herniated disc” are often used interchangeably even though there are subtle differences.

DOME – The round balloon-like portion of the aneurysm which usually arises from the artery from a smaller portion called the neck of the aneurysm.

DOPPLER – A non-invasive study that uses sound waves to show the flow in a blood vessel and can be used to determine the degree of narrowing (percent stenosis) of the vessel. A wand is placed on the skin over the vessel that is to be imaged. This study has no risks and is not painful.

DURA – Dura mater.

DURA MATER – A tough fibrous membrane that covers the brain and spinal cord, but is separated from them by a small space. It is the outermost layer of the three membranes.

DYSESTHESIA – A condition in which ordinary touch, temperature or movement produces a disagreeable sensation.

DYSPHASIA – Difficulty in the use of language due to a brain lesion without mental impairment.

DYSTONIA MUSCULORM DEFORMANS – An affliction, occurring especially in children, marked by muscular contractions producing distortions of the spin and hips.


EDEMA – An excessive accumulation of fluid generally in the extracellular or intracellular areas of the brain.

ELECTROENCEPHALOPGRAHY (EEG) – The study of the electrical currents set up by brain actions; the record made is called an electroencephalogram.

ELECTROMYOGRAPHY (EMG) – A method of recording the electrical currents generated in a muscle during its contraction.

ENDARTERECTOMY – Removal of fatty or cholesterol plaques and calcified deposits from the internal wall of an artery.

ENDOCRINE GLAND – A gland that furnishes an internal secretion, usually having an effect on another organ.

ENDOCRINOPATHY – Any disease due to abnormality of quantity or quality in one or more of the internal glandular secretions.

EPENDYMA – The membrane lining the cerebral ventricles of the brain and central canal of the spinal cord.

EPENDYMOMA – A growth in the brain or spinal cord arising from ependymal tissue.

EPIDURAL – Immediately outside the dura mater. Same as extradural. Also form of local analgesia and anesthesia often injected into the outer section of the spinal canal.

EPIDURAL HEMATOMA – A blood clot between the dura mater and the inside of the skull.

EPILEPSY – Disorder characterized by abnormal electrical discharges in the brain, causing abnormal sensation, movement or level of consciousness.


FALX (CEREBRI) – An extension of dura between the right and left hemispheres of the brain.

FONTANELLE – Normal openings in the skull of infants; the largest of these is the anterior fontanel or “soft spot” in the middle of the head.

FORAMINOTOMY – Surgical opening or enlargement of the bony opening traversed by a nerve root as it leaves the spinal canal.

FUSIFORM ANEURYSM – a sausage-like enlargement of the vessel


GALACTORRHEA – The discharge of milk from the breasts unassociated with nursing or childbirth.

GAMMA KNIFE – Equipment that precisely delivers a concentrated dose of radiation to a predetermined target using gamma rays.

GCS – Glasgow Coma Scale.

GLASGOW COMA SCALE – The most widely used system of classifying the severity of head injuries or other neurologic diseases.

GLASGOW OUTCOME SCALE – A widely used system of classifying outcome after head injury or other neurologic diseases.

GLIA (Also termed neuroglia) – The major support cells of the brain. These cells are involved in the nutrition and maintenance of the nerve cells.

GLIOMA – A tumor formed by glial cells.

GLIOBLASTOMA – A rapidly growing tumor composed of primitive glial cells, mainly arising from astrocytes.

GLOBUS PALLIDUS – Part of the basal ganglia, which are brain cells that lie deep in the brain.


HEMANGIOMA – An aggregation of multiple, dilated, blood vessels.

HEMATOMA – A collection of blood outside the blood vessels.

HEMIANOPIA – Loss of vision of one-half of the visual field.

HEMIATROPHY – Atrophy of half of an organ or half of the body.

HEMIPLEGIA – Paralysis of one side of the body.

HEMORRHAGE – Bleeding due to the escape of blood from a blood vessel.

HERNIATED NUCLEUS PULPOSUS (HNP) – Extrusion of the central portion of an intervertebral disc through the outer cartilaginous ring. The material can compress the spinal cord or nerves in or exiting the spinal canal.

HORMONE – A chemical substance formed in one gland or part of the body and carried by the blood to another organ, which it stimulates to functional activity.

HYDROCEPHALUS – A condition, often congenital, marked by abnormal and excessive accumulation of cerebrospinal fluid in the cerebral ventricles. This dilates the ventricles and, in infants and young children, causes the head to enlarge.

HYDROMYELIA – Expansion of the spinal cord due to increased size of the central canal of the cord, which is filled with CSF.

HYPERACUSIS – Abnormal acuteness of hearing or auditory sensation.

HYPERESTHESIA – Excessive sensibility to touch, pain or other stimuli.

HYPERTENSION – High blood pressure.

HYPOTHALAMUS – A collection of specialized nerve cells at the base of the brain that controls the anterior and posterior pituitary secretions, and is involved in other basic regulatory functions such as temperature control and attention.


INFUNDIBULUM – A stalk extending from the base of the brain to the pituitary gland.

INTRA-AORTIC BALLOON COUNTER PULSATION DEVICE – This device is a pump that is inserted into the main vessel of the body (the aorta) to help the heart deliver blood to critical organs such as the brain or kidneys.

INTRA-ARTERIAL CATHETERIZATION ANGIOGRAPHY – An invasive study in which a catheter (a small tube) is placed in the artery and contrast material is injected to which makes the blood vessels visible on an X-Ray image. The catheter is inserted in the groin into the femoral artery (the artery to the leg) through a needle, and is guided into the arteries in the neck and head.

INTRACEREBRAL HEMATOMA – A blood clot within the brain.

INTRACRANIAL PRESSURE (ICP) – The overall pressure inside the skull.

INTRAOPERATIVE CISTERNOGRAPHY – Administration of a contrast dye into the ventricles, which are chambers in the brain that contain brain fluid.

ISCHEMIA – Inadequate circulation of blood generally due to a blockage of an artery.


JUGULAR VEINS – The major veins on each side of the neck draining blood from the head towards the heart.


LABYRINTH – The internal ear, comprised of the semi-circular canals, vestibule and cochlea.

LAMINA – The flattened or arched part of the vertebral arch, forming the roof of the spinal canal.

LAMINECTOMY – Excision of one or more laminae of the vertebrae.

LAMINOTOMY – An opening made in a lamina.

LEPTOMENINGES – Two thin layers of fine tissue covering the brain and spinal cord: the pia mater and arachnoid.

LEPTOMENINGITIS – Inflammation of the membranes covering the brain and spinal cord.

LEUKODYSTROPHY – Disturbance of the white matter of the brain.

LEUKOENCEPHALITIS – An inflammation of the white matter of the brain.

LINEAR ACCELERATOR – Equipment that precisely delivers a concentrated dose of radiation to a predetermined target using X-rays.

LIPOMA – A benign fatty tumor, usually composed of mature fat cells.

LORDOSIS – Curvature of the spine with the convexity forward.

LUMBAR DRAIN – A device (usually a long, thin, flexible tube) inserted through the skin into the cerebrospinal fluid space of the lower back; provides a method of draining cerebrospinal fluid.


MAGNETIC RESONANCE ANGIOGRAPHY (MRA) – A non-invasive study that is conducted in a magnetic resonance imager (MRI). The magnetic images are assembled by a computer to provide an image of the arteries in the head and neck.

MAGNETIC RESONANCE IMAGING (MRI) – Diagnostic test that produces three-dimensional images of body structures using powerful magnets and computer technology rather than X-rays.

MEDIAN NERVE – The nerve formed from the brachial plexus that supplies muscles in the anterior forearm and thumb, as well as sensation of the hand. It may be compressed or trapped at the wrist in carpal tunnel syndrome.

MEDULLOBLASTOMA – Tumor composed of medulloblasts, which are cells that develop in the roof of the fourth ventricle (medullary velum).

MENINGES – The three membranes covering the spinal cord and brain termed dura mater, arachnoid mater and pia mater.

MENINGIOMA – A firm, often vascular, tumor arising from the coverings of the brain.

MENINGITIS – An infection or inflammation of the membranes covering the brain and spinal cord.

MENINGOCELE – A protrusion of the coverings of the spinal cord or brain through a defect in the skull or vertebral column.

MENINGOENCEPHALITIS – An inflammation or infection of the brain and meninges.

MENINGOENCEPHALOCELE – A protrusion of both the meninges and brain tissue through a skull defect.

MRA – Magnetic Resonance Angiography. A non-invasive study that is conducted in a magnetic resonance imager (MRI). The magnetic images are assembled by a computer to provide an image of the arteries in the head and neck.

MRI – Magnetic Resonance Imaging – Scanning technique for views of the brain or spinal cord. No radiation is involved, but rather pulsed magnetic waves used to delineate the structures within the brain.

MYELIN – The fat-like substance that surrounds the axon of nerve fibers and forms an insulating material.

MYELOGRAM – An x-ray of the spinal canal following injection of a contrast material into the surrounding cerebrospinal fluid spaces.

MYELOPATHY – Any functional or pathologic disturbance in the spinal cord.

MYELOMENINGOCELE – A protrusion of the spinal cord and its coverings through a defect in the vertebral column.

MYOPATHY – Any disease of muscle.


NEURALGIA – A paroxysmal pain extending along the course of one or more nerves.

NEURECTOMY – Excision of part of a nerve.

NEURITIS – Inflammation of a nerve; may also be used to denote non-inflammatory nerve lesions of the peripheral nervous system.

NEUROBLASTOMA – Tumor of sympathetic nervous system, found mostly in infants and children.

NEUROFIBROMA – A tumor of the peripheral nerves due to an abnormal collection of fibrous and insulating cells.

NEUROFIBROMATOSIS – A familial condition characterized by developmental changes in the nervous system, muscles and skin, marked by numerous tumors affecting these organ systems.

NEUROHYPOPHYSIS – The posterior lobe of the pituitary gland.

NEUROLYSIS – Removal of scar or reactive tissue from a nerve or nerve root.

NEUROMA – A tumor or new growth largely made up of nerve fibers and connective tissue.

NEUROPATHY – Any functional or pathologic disturbance in the peripheral nervous system.

NYSTAGMUS – Involuntary rapid movement of the eyes in the horizontal, vertical or rotary planes of the eyeball.


OCCIPUT – The back part of the head.

OLIGODENDROGLIA – Non-nerve cells (see glia) forming part of the supporting structure of the central nervous system.

OLIGODENDROGLIOMA – A growth of new cells derived from the oligodendroglia.

OPHTHALMOPLEGIA – Paralysis of one or more of the eye muscles.

OSTEOMA – A benign tumor of bone.

OSTEOMYELITIS – Inflammation of bone due to infection, which may be localized or generalized.


PAPILLEDEMA – Swelling of the optic nerve head that can be seen in the back of the retina during eye examination.

PARAPLEGIA – Paralysis of the lower part of the body including the legs.

PERITONEAL CAVITY – Body cavity in which the abdominal organs are situated.

PITUITARY– Gland at base of the brain that secretes hormones into the blood stream. Those hormones then regulate other glands including the thyroid, adrenals and gonads. The “Master Gland”.

POLYNEURITIS – Inflammation of two or more nerves simultaneously.

PORENCEPHALY – Abnormal cavity within brain tissue, usually resulting from outpouching of a lateral ventricle.

POST-ICTAL (POSTICTAL) – State following a seizure, often characterized by altered function of the limbs and/or mentation.

PROPRIOCEPTION – Sensation concerning movements of joints and position of the body in space.

PSEUDOTUMOR CEREBRI – Raised intracranial pressure, usually causing only headache and papilledema. No clear underlying structural abnormality.

PUPIL – The black part of the eye through which light enters; enlarges in dim light and decreases in size in bright light.


QUADRANTANOPIA – Defect in vision or blindness in one fourth of the visual field.

QUADRIPLEGIA – Paralysis of all four limbs.


RACHISCHISIS – Abnormal congenital opening of the vertebral column.

RADIATION ONCOLOGIST – A medical doctor who has received advanced training in the treatment of persons receiving X-ray treatment for an illness.

RADIATION PHYSICIST – A person having a PhD degree trained in the science dealing with the properties, changes and interactions of continuous energy.

RADIOLOGIST – A medical doctor who has received specialized training in interpreting X-rays, CTs, MRIs and performing angiography.

RADIOTHERAPY – Treatment of a lesion with radiation.


SACCULAR ANEURYSM – A balloon-like outpouching of a vessel (the more common type of aneurysm).

SCOTOMA – An area of decreased vision surrounded by an area of less depressed or normal vision.

SHUNT – A tube or device implanted in the body to divert excess CSF away from the brain to another place in the body.

SPINA BIFIDA – A congenital defect of the spine marked by the absence of a portion of the spine.

SPINAL FUSION – Operative method of strengthening and limiting motion of the spinal column that can be performed with a variety of metal instruments and bone grafts or bone grafts alone.

SPONDYLOLISTHESIS – Forward displacement of one vertebra on another.

SPONDYLOSIS – Degenerative bone changes in the spine usually most marked at the vertebral joints.

STENOSIS – Narrowing.

STEREOTACTIC – Originated from the Greek words stereo meaning three dimensional and tactos meaning touched.

STEREOTACTIC RADIOSURGERY – The precise delivery of radiation to a preselected stereotactically localized target.

STRABISMUS – Deviation of eye movement that prevents the two eyes from moving in a parallel fashion.

SUBARACHNOID HEMORRHAGE – Blood in, or bleeding into, the space under the arachnoid membrane, most commonly from trauma or from rupture of an aneurysm.

SUBDURAL HEMATOMA – A collection of blood (clot) trapped under the dura matter, the outermost membrane surrounding the brain and spinal cord.

SYRINGOMYELIA – A fluid filled cavity in the spinal cord.


TERATOMA – Tumor or growth made up of several different types of tissue (i.e. fat, bone, muscle, skin).

THROMBUS – A blood clot attached to the wall of an artery.

THALAMUS – Brain cells which lie in the upper part of the brainstem.

TIC DOULOUREUX – (See trigeminal neuralgia.)

TRANSSPHENOIDAL APPROACH – Operative method of reaching the pituitary gland or skull base traversing the nose and sinuses.

TRIGEMINAL NEURALGIA – Paroxysmal pain in the face. Pain may be so severe that it causes an involuntary grimace or “tic”. Also called Tic Douloureux.


ULTRASOUND – The use of high-frequency sound to create images of internal body structures.


VALVE – Device placed in a shunt system to regulate the rate and direction of CSF flow.

VASOCONSTRICTION – A decrease in the diameter of blood vessels.

VASODILATATION – An increase in the diameter of blood vessels.

VASOPRESSIN – A hormone secreted by the hypothalamus and stored in the posterior pituitary that raises blood pressure and increases re-absorption of water by the kidneys.

VASOPRESSOR – An agent that constricts the arteries and raises blood pressure.

VASOSPASM – Spasm of blood vessels, decreasing their diameter.

VENTRICLE – The cavities or chambers within the brain that contain the cerebrospinal fluid. There are two lateral ventricles and midline third and fourth ventricles.

VENTRICULITIS – Inflammation and/or infection of the ventricles.

VENTRICULOGRAM – An x-ray study of the ventricles.

VENTRICULOSTOMY – An opening into the ventricles of the brain, achieved by inserting a small, thin, hollow catheter. Serves as a means to relieve pressure from the brain and spinal cord.

VENTRICULAR DRAINAGE – Insertion of a small tube into the ventricles to drain cerebrospinal fluid, usually performed when pressure is increased.

VERMIS – Middle part of the cerebellum between the two hemispheres.

VERTEBRA– Any of the 33 bones of the spinal column.

VERTIGO – An abnormal sensation of rotation or movement of one’s self or the environment.


X-RAY – Application of electromagnetic radiation to produce a film or picture of a bone or soft-tissue area of the body.

The AANS does not endorse any treatments, procedures, products or physicians referenced in these patient fact sheets. This information is provided as an educational service and is not intended to serve as medical advice. Anyone seeking specific neurosurgical advice or assistance should consult his or her neurosurgeon, or locate one in your area through the AANS’ Find a Board-certified Neurosurgeon” online tool.