Every so often it is good to review the basics -- especially when they keep changing on you!
Below is a good introduction to the changing definition of the concept of disability. This is an especially good read for those in the US who feel they are familiar with the Americans with Disabilities Act (ADA). There are some better adapted definitions ut there than the one codified in ADA.
World Health Organization's New Definition of Disability
The way disability is defined and understood has also changed in the last decade. Disability was once assumed as a way to characterize a particular set of largely stable limitations. Now the World Health Organization (WHO) has moved toward a new international classification system, the International Classification of Functioning, Disability and Health (ICF 2001). It emphasizes functional status over diagnoses. The new system is not just about people with traditionally acknowledged disabilities diagnostically categorized but about all people. For the first time, the ICF also calls for the elimination of distinctions, explicitly or implicitly, between health conditions that are 'mental' or 'physical.'
The new ICF focuses on analyzing the relationship between capacity and performance. If capacity is greater than performance then that gap should be addressed through both removing barriers and identifying facilitators. The new WHO ICF specifically references Universal Design as a central concept that can serve to identify facilitators that can benefit all people.
The WHO defines disability as a contextual variable, dynamic over time and in relation to circumstances. One is more or less disabled based on the interaction between the person and the individual, institutional and social environments. The ICF also acknowledges that the prevalence of disability corresponds to social and economic status. The 2001 ICF provides a platform that supports Universal Design as an international priority for reducing the experience of disability and enhancing everyone's experience and performance.