The World Health Organization (WHO) suggested the following definitions in 1980:

Impairment: a loss or abnormality of psychological, physiological, or anatomical structure or function.

Disability: any restriction or lack (resulting from an impairment) of the ability to perform an activity in the manner or within the range considered normal for a human being.

Handicap: a disadvantage for a given individual, resulting from an impairment or a disability, that limits or prevents the fulfilment of a role that is normal (depending on age, sex, and social and culture factors) for that individual.

Impairments and disabilities may be temporary or permanent, reversible or irreversible, and progressive or regressive. The situation people find themselves in may determine to what degree a disability is handicapping for them. It is evident from the definitions above that a handicap is the result both of an impairment and of environmental conditions. If environmental barriers are taken away, the person will still be impaired, but not necessarily handicapped. It should also be noted that the definition of disability as distinct from handicap is not without problems, in particular the formulation "considered normal for a human being", and many people with disabilities do not distinguish their use.

The functional ability of people who are diagnosed as having the same impairment or disability may vary widely. For example, some people who are legally blind may be able to utilize differences in light intensity, while others are unable to perceive such differences. People who have clinically similar hearing impairments, as shown on audiograms, may use quite different aspects of the acoustic information available to them. The degree of handicap may vary significantly and may be specific to certain situations.

In this brief review of impairment and disability, differences in degree are dealt with only in a very general manner. The emphasis is on typical features rather than variations. However, when assessing the needs of a single individual, variation that may influence the handicapping effects of the condition must be taken into account.

Letís use the terms above to explain the differences:

         Physical impairment pertains to a loss of an anatomical structure; for the benefit of this exercise, letís say the person lost a leg due to an accident. He can wear prosthetics as a replacement of the lost leg.

         Physical disability now refers to the inability to walk. To be able to navigate the surroundings, the person can use a wheelchair.

         Physical handicap now means that this person faces disadvantages that prevent him or her to perform a normal role in life, such as not being able to climb stairs anymore. Or run a marathon. Or be a basketball player. Here is where the environment plays a part. By providing wheelchair access or lift for the person with physical disability, he or she will have no problem going up to the next floors of a building. By providing multi-sport events for athletes with physical disabilities, such as Paralympics, the person will still able to participate in sports.