According to many definitions, a disability or functional impairment is an impairment that may be cognitive, developmental, intellectual, mental, physical, sensory, or some combination of these. Other definitions describe disability as the societal disadvantage arising from such impairments. Disability substantially affects a person's life activities and may be present from birth or occur during a person's lifetime.
Disabilities is an umbrella term, covering impairments, activity limitations, and participation restrictions. An impairment is a problem in body function or structure; an activity limitation is a difficulty encountered by an individual in executing a task or action; while a participation restriction is a problem experienced by an individual in involvement in life situations. Disability is thus not just a health problem. It is a complex phenomenon, reflecting the interaction between features of a person’s body and features of the society in which he or she lives.
Disability is a contested concept, with different meanings in different communities. The term disability may be used to refer to physical or mental attributes that some institutions, particularly medicine, view as needing to be fixed (the medical model); it may also refer to limitations imposed on people by the constraints of an ableist society (the social model); or the term may serve to refer to the identity of disabled people. Physiological functional capacity (PFC) is a measure of an individual's performance level that gauges one's ability to perform the physical tasks of daily life and the ease with which these tasks are performed. PFC declines with advancing age to result in frailty, cognitive disorders, or physical disorders, all of which may lead to labeling individuals as disabled.
- Handicap has been disparaged as a result of false folk etymology that claims it is a reference to begging. The term is actually derived from an old game, Hand-i'-cap, in which two players trade possessions and a third, neutral person judges the difference of value between the possessions. The concept of a neutral person evening up the odds was extended to handicap racing in the mid-18th century. In handicap racing, horses carry different weights based on the umpire's estimation of what would make them run equally. The use of the term to describe a person with a disability – by extension from handicap racing, a person carrying a heavier burden than normal – appeared in the early 20th century.
- The ability to go places and do things. People with certain types of disabilities struggle to get equal access to some things in society. For example, a blind person cannot read printed paper voting ballots, and therefore does not have access to voting that requires paper ballots.
- A change that improves access. For example, if voting ballots are available in Braille or on a text-to-speech machine, or if another person read the ballot to the blind person and recorded the choices, then the blind person would have access to voting.