A disability is defined as any condition that makes it more difficult for a person to do particular tasks or interact with the environment around them in an efficient manner (socially or materially). These disorders, or impairments, may be caused by cognitive, developmental, intellectual, mental, physical, or sensory causes, or by a combination of many factors.. Disabilities may be caused by impairments that are present from birth or can be acquired throughout the course of a person's lifetime. According to the United Nations Convention on the Rights of Persons with Disabilities, disability is defined as follows:
The presence of long-term physical, mental, intellectual, or sensory impairments that, when combined with other factors, may make it difficult for [a person] to participate fully and effectively in society on an equal footing with others.
Disability is a contentious term, having varying interpretations in various cultures and contexts. It has been referred to as a "embodied difference," but the word may also apply to physical or mental characteristics that certain institutions, especially medicine, consider to be undesirable and should be eliminated (the medical model). It may also refer to the limits placed on people as a result of the constraints of an ableist society (the social model), or it may relate to the identification of persons who are physically or mentally handicapped. Physiological functional capacity (PFC) is a measure of an individual's ability to execute the physical activities of daily living and the ease with which these tasks are completed. It is used to assess an individual's overall performance level. With age, PFC diminishes, which may result in frailty, cognitive problems, or physical illnesses, all of which may lead to people being labelled as handicapped by society. Globally, according to the World Report on Disability, about 1 billion individuals, or 15 percent of the world's population, are afflicted by disability. In nature, a handicap may be clearly apparent or it may be completely unseen.