Frailty is an evolving concept that is generally defined in biomedical or psychosocial terms. It is not necessarily related to a specific single disease process. Passing by the theories of Selye (1936) on the exhaustion of the General Adaptation Syndrome,until reaching to the studies of Fried (2001) who, firstly, proposed diagnostic criteria for frailty, in this paper are explored different ways to understand this concept, until endeavour to give a possible modern view. The definition of a frailty syndrome characterized by a multi-system reduction in ?reserve capacity? remains widely accepted.