Each WHOQOL facet can be characterised as a description of a behaviour, a state of being, a capacity or potential or a subjective perception or experience. For example, pain is a subjective perception or experience; fatigue may be defined as a state; mobility may be defined either as a capacity (ability to move around) or as a behaviour (actual report of walking). A definition was written for each of the facets of quality of life covered by the WHOQOL assessment.