Glossary

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Flare(also: Symptom Flare, Flare-Up)

A temporary but often significant worsening of symptoms associated with a chronic illness, which can last from hours to weeks. Flares can be triggered by environmental factors (heat, pollen, weather changes), physical exertion, stress, illness, or unpredictable internal…

Frontotemporal Dementia(also: FTD, Frontotemporal Lobar Degeneration, Pick's Disease)

A group of disorders caused by progressive degeneration of the frontal and temporal lobes of the brain, primarily affecting personality, behavior, and language. Unlike Alzheimer's disease, frontotemporal dementia often begins before age 60 and initially impacts executive…

Gait Disturbance(also: Gait Abnormality, Gait Impairment, Gait Deviation)

Any deviation from a person's normal walking pattern, including decreased walking velocity, reduced step and stride length, increased step time, asymmetrical gait, and instability. Gait disturbances can result from neurological conditions (multiple sclerosis, Parkinson's…

Glasgow Coma Scale(also: GCS)

A standardized neurological assessment scale used to evaluate the severity of brain injuries by measuring three aspects of responsiveness: eye opening (1-4 points), verbal response (1-5 points), and motor response (1-6 points), yielding a total score from 3 to 15. A GCS score of…

Glaucoma

A group of eye diseases that damage the optic nerve, usually caused by abnormally high intraocular pressure. It is one of the leading causes of irreversible blindness worldwide, affecting over 80 million people. Glaucoma typically causes gradual peripheral vision loss that may…

Glaucoma

A group of eye conditions that damage the optic nerve, typically associated with elevated intraocular pressure. Glaucoma is a leading cause of irreversible blindness worldwide. It usually causes gradual loss of peripheral vision first, which can progress to tunnel vision and…

Hearing Loss(also: Hearing Impairment, Hard of Hearing, Deafness)

A partial or total inability to hear sounds, ranging from mild hearing loss to profound deafness. Hearing loss can be congenital or acquired, and becomes increasingly common with age, affecting approximately one-third of people over 65. Digital accessibility for people with…

Hearing loss(also: Hearing impairment, Hard of hearing, Deafness spectrum)

A reduction in the ability to perceive sounds, occurring on a spectrum from mild (difficulty hearing soft sounds or speech in noisy environments) through moderate and severe to profound (inability to hear most sounds without amplification). Hearing loss may be unilateral (one…

Hemiplegia(also: Hemiparesis)

A condition involving paralysis or severe weakness on one side of the body, most commonly resulting from stroke but also caused by traumatic brain injury, cerebral palsy, or other neurological conditions. Hemiplegia affects the arm, leg, and sometimes facial muscles on the…

Homebound(also: Housebound)

A status in which an individual has difficulty leaving their home without assistive devices or help from others, typically due to illness, injury, or environmental factors such as lack of transportation. As defined by the U.S. Centers for Medicare & Medicaid Services, homebound…

Intellectual and Developmental Disability(also: IDD, Intellectual Disability, Developmental Disability)

A group of conditions characterised by significant limitations in both intellectual functioning (reasoning, learning, problem-solving) and adaptive behaviour (everyday social and practical skills), with onset during the developmental period. IDD encompasses a wide range of…

Intention Tremor(also: Cerebellar Tremor, Action Tremor)

A type of tremor that appears or worsens during voluntary, goal-directed movement — particularly as a limb approaches its target — and is typically absent at rest. Intention tremor is most often caused by damage to the cerebellum or its pathways (multiple sclerosis, stroke,…

Late-Life Disability(also: Age-Related Disability, Acquired Age-Related Disability)

Disability that develops gradually as a person ages, including changes in vision, hearing, motor control, and cognition. Unlike disabilities present from birth or acquired through injury, late-life disabilities often develop incrementally, and individuals may not identify as…

Legal Blindness(also: Legally Blind)

A level of vision loss defined in many countries as visual acuity of 20/200 or less in the better eye with best correction, or a visual field of 20 degrees or less. Legal blindness does not necessarily mean total blindness — many legally blind people have some residual or…

Lewy Body Dementia(also: LBD, Dementia with Lewy Bodies, DLB)

A type of progressive dementia caused by abnormal protein deposits called Lewy bodies in the brain. Lewy body dementia affects thinking, movement, behavior, and mood, and is the third most common cause of dementia after Alzheimer's disease and vascular dementia. Symptoms include…

Loudness Recruitment(also: Recruitment, Hyperacusis-like Recruitment)

Loudness recruitment is a common consequence of sensorineural hearing loss in which the range between 'just audible' and 'uncomfortably loud' sounds is compressed — quiet sounds are harder to hear, but sounds above threshold grow louder more rapidly than in a typical listener.…

Low Vision(also: Partial Sight, Partially Sighted)

A visual impairment that cannot be fully corrected by glasses, contact lenses, medication, or surgery, but where some usable vision remains. Low vision encompasses a wide range of conditions and severity levels, typically defined as visual acuity between 20/70 and 20/400 in the…

Macular Degeneration(also: AMD, Age-Related Macular Degeneration, ARMD)

A progressive eye condition affecting the macula — the central part of the retina responsible for sharp, detailed vision. It is the leading cause of severe vision loss in people over 50 in developed countries. Macular degeneration gradually destroys central vision while…

Macular degeneration(also: AMD, Age-related macular degeneration, ARMD)

A progressive eye disease that damages the macula, the central part of the retina responsible for sharp, detailed vision. It is the leading cause of vision loss in people over 50, affecting central vision while typically leaving peripheral vision intact. This means people with…

Mild Cognitive Impairment(also: MCI)

A condition involving a noticeable decline in cognitive abilities — including memory, reasoning, or judgment — that is greater than expected for a person's age but does not significantly interfere with daily functioning. MCI is distinct from dementia in that individuals…

Mild cognitive impairment(also: MCI)

A condition involving a noticeable decline in cognitive abilities — such as memory or thinking skills — that is greater than expected for a person's age but does not significantly interfere with daily independent functioning. MCI is not classified as dementia, and in some cases…

Mobility Impairment(also: Mobility Disability, Physical Mobility Limitation)

A condition that limits a person's ability to move freely and independently, affecting functions such as walking, climbing stairs, or maintaining balance. Mobility impairments can result from congenital conditions, spinal cord injuries, amputations, neurological conditions like…

Motor Neuron Disease(also: MND, ALS, Amyotrophic Lateral Sclerosis)

A group of progressive neurological disorders that destroy motor neurons, the cells controlling voluntary muscle activity including speaking, walking, breathing, and swallowing. ALS (amyotrophic lateral sclerosis) is the most common form. As the disease progresses, people lose…

Motor Skill(also: Motor Skills, Gross Motor Skill, Fine Motor Skill)

A motor skill is a learned ability to produce a coordinated movement of muscles to achieve an outcome, ranging from gross-motor actions like walking, jumping, and balancing to fine-motor actions like handwriting, buttoning a shirt, or manipulating a stylus. Motor skills strongly…

Motor speech disorder(also: MSD)

A category of speech disorders caused by neurological impairments affecting the motor planning, programming, or execution of speech movements. Motor speech disorders include dysarthria (muscle weakness or paralysis) and apraxia of speech (difficulty coordinating voluntary speech…

Multimorbidity(also: Multiple Long-term Conditions, Co-occurring Conditions)

Multimorbidity is the presence of two or more chronic health conditions or long-term impairments in a single individual. It is especially prevalent among older adults and is a major factor in the complexity of accessibility needs. Research shows that multimorbidity is the norm…

Multiple sclerosis(also: MS)

A progressive disease of the central nervous system caused by the immune system attacking the protective myelin sheath around nerve fibres, causing them to fail or misfire. The randomness of the damage means that symptoms vary widely between individuals and over time, including…

Muscular Dystrophy(also: MD)

A group of inherited genetic conditions that cause progressive weakness and loss of muscle mass, affecting mobility, upper limb function, and in some forms, respiratory and cardiac function. People with muscular dystrophy often rely on electric wheelchairs for mobility and may…

Muscular Dystrophy(also: MD)

A group of inherited genetic conditions that cause progressive weakness and degeneration of skeletal muscles, the muscles that control movement. There are many types of muscular dystrophy varying in severity, age of onset, and which muscles are affected. Because muscular…

Neurodivergence(also: Neurodiversity, Neurodivergent)

The natural variation in human neurological development and functioning that includes conditions such as autism, ADHD, dyslexia, anxiety disorders, intellectual disabilities, and other neurological differences. The neurodiversity paradigm frames these differences as natural…

Neurodiversity(also: Neurological diversity)

A concept that regards differences in brain function and behavioural traits — including autism, ADHD, dyslexia, dyspraxia, and intellectual disability — as natural variation within the human population rather than deficits or disorders. The term emerged from autistic…

Nonverbal Learning Disorder(also: NVLD, Nonverbal Learning Disability, NLD)

A neurodevelopmental condition characterized by difficulties with visual-spatial processing, motor coordination, and social skills, while verbal abilities are typically a relative strength. People with NVLD may struggle with interpreting visual information, understanding spatial…

Nystagmus(also: Involuntary eye movement, Dancing eyes)

A condition characterized by involuntary, repetitive, rhythmic movements of the eyes, which may move side to side (horizontal), up and down (vertical), or in a circular pattern (rotary). Nystagmus can be congenital (present from birth) or acquired later in life due to…

Nystagmus(also: Involuntary Eye Movement, Dancing Eyes)

A condition involving involuntary, repetitive, and rhythmic movements of the eyes, which can be horizontal, vertical, or rotary. Nystagmus can be congenital (present from birth) or acquired later in life due to neurological conditions, medications, or other causes. It often…

Oligodactyly

A congenital condition in which a person is born with fewer than the typical number of fingers or toes. The condition varies widely in presentation — some individuals may have fewer digits on one hand or both, and the remaining digits may differ in size, strength, or dexterity.…

Osteoarthritis(also: OA, Degenerative Joint Disease)

The most common form of arthritis, caused by progressive breakdown of the cartilage that cushions the ends of bones. Osteoarthritis produces joint pain, stiffness, swelling, and reduced range of motion, most often in the hands, knees, hips, and spine. For digital accessibility,…

PTSD(also: Post-traumatic stress disorder, Post-traumatic stress)

A psychiatric condition that can develop after exposure to traumatic events, characterized by intrusive memories, avoidance of trauma-related stimuli, negative changes in mood and cognition, and heightened arousal responses including hypervigilance and exaggerated startle. In…

Paralysis(also: Paralyzed, Paresis)

The partial or complete loss of voluntary muscle function, resulting from damage to the motor nervous system. Common causes include spinal cord injury, stroke, traumatic brain injury, motor neuron diseases such as ALS, multiple sclerosis, cerebral palsy, and brainstem lesions…

Partial Trisomy 9p(also: 9p Duplication Syndrome, Rethore Syndrome)

A rare chromosomal condition in which a portion of the short arm of chromosome 9 is present in triplicate rather than in duplicate. The condition is associated with intellectual disability, distinctive craniofacial features, developmental delay, and in many cases co-occurring…

People with Dementia(also: PwD)

A person-first term used in accessibility and dementia research to refer to individuals living with dementia — an umbrella term covering progressive neurological conditions (such as Alzheimer's disease, vascular dementia, Lewy body dementia, and frontotemporal dementia) that…

People with Severe Motor Disabilities(also: PSMD)

A term used in assistive technology and human-robot interaction research to describe individuals whose motor impairments are severe enough that they cannot reliably use their hands or arms for everyday tasks, and who therefore depend on hands-free control modalities such as eye…

Peripheral Neuropathy(also: Neuropathy)

Peripheral neuropathy is a condition resulting from damage to the peripheral nerves, which carry signals between the brain, spinal cord, and the rest of the body. Symptoms typically include numbness, tingling, weakness, and pain, most commonly in the hands and feet. For…

Phonophobia(also: Sound Phobia, Ligyrophobia)

Phonophobia is an intense fear or aversion to specific sounds or loud noises that goes beyond simple discomfort, often leading to avoidance behaviors such as fleeing from environments where triggering sounds may occur. Unlike hyperacusis (heightened sensitivity to sound volume)…

Photosensitive epilepsy(also: PSE, Photosensitivity, Visually-provoked epilepsy)

A form of epilepsy in which seizures are triggered by visual stimuli such as flashing lights, strobing effects, rapid colour transitions, or high-contrast repeating patterns. It affects approximately 3 to 5 percent of people with epilepsy and is more common in children and…

Photosensitivity(also: Light Sensitivity, Photophobia)

An abnormal sensitivity to light that can cause discomfort, pain, or visual disturbance. Photosensitivity affects many people with visual impairments and certain neurological conditions including migraine and epilepsy. In digital accessibility, photosensitivity considerations…

Post-Exertion Malaise(also: PEM, Post-Exertional Malaise, Crash)

A disproportionate worsening of symptoms following physical, cognitive, or emotional exertion that would not cause comparable effects in a healthy person. Post-exertion malaise is a hallmark symptom of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and occurs in…

Post-Traumatic Stress Disorder(also: PTSD)

A mental health condition that can develop after experiencing or witnessing a traumatic event such as violence, natural disaster, serious accident, or combat. Symptoms include intrusive memories or flashbacks, avoidance of trauma-related stimuli, negative changes in thinking and…

Post-lingual Deafness(also: Post-linguistic Deafness, Acquired Deafness, Late-Onset Deafness)

Deafness that occurs after a person has acquired spoken language, meaning they have existing literacy in written and spoken language. Post-lingual deaf users can typically read and write fluently, making text-based accessibility features like captions and transcripts highly…

Postlingual Deafness(also: Postlingually Deaf, Acquired Hearing Loss)

Hearing loss that occurs after a person has acquired spoken language, typically after about age three to five. Postlingually deaf people usually retain spoken-language fluency, literacy, and memory of sound, which affects their rehabilitation trajectory and their experience of…

Pre-lingual Deafness(also: Pre-linguistic Deafness, Congenital Deafness)

Deafness that occurs before a person acquires spoken language, either present from birth or developing in early childhood. People with pre-lingual deafness typically use sign language as their primary means of communication and may have limited literacy in written/spoken…