A person is said to have a disability if they find it difficult or impossible to perform one or more activities of everyday living.
Until recently, little distinction was made between the physical or mental condition of a person and the difficulties they faced. In the past 20 years, the social model of disability has been developed, which alters this perception. It distinguishes between an impairment (some ability is objectively less than average) and a deviation from the average that by itself is not better or worse, but that is a problem due to the attitude of society or the fact that standard facilities are based on the average, and that there is a the lack of tools.
For example, as recently as the 1960s, left-handedness was seen as an abnormality. In schools in the Western world, left-handed children were forced to write with their right hand and punished if they did not comply. By the 1980s, left-handedness was accepted as simply a difference; a physical characteristic. Yet if tools such as scissors and corkscrews are only available in their right-handed forms, a left-handed person finds themselves disabled: they are unable to perform certain tasks and must be assisted by another person.
Thus, in the social model of disability, the disability is caused by society and the physical environment. Someone who is unable to walk and needs a wheelchair has an impairment; however, the social exclusion they may experience (lack of accessible transport, no adapted public toilets, buildings which are innaccessible) is caused by their environment, not their physical condition.
The term handicapped, in its origin, meant hand in cap, and had its origins in sport and gambling.
Some disabled persons apply the term tab for the "nondisabled", meaning "temporarily able-bodied".
Various attributive forms, such as "the disabled", "the blind", "the deaf", etc. -- rather than "disabled persons", "blind persons", "deaf persons", etc. -- are considered objectionable by many persons, since the former labeling seems to characterize a person by a single attribute.
Many of the most famous or creative persons in history have been disabled persons .