In this paper we will provide an overview of various models, definitions, and criteria proposed for furthering our understanding of frailty but we will not systematically evaluate and compare them. Models are descriptions or analogies that are used to help us visualize something that typically cannot be directly observed. They are at an abstract or conceptual level.
Definitions are statements expressing the essential nature of something. They should make our understanding of the topic both definite and clear. Criteria are operational definitions that outline the characterizing traits of an entity. There are overlaps and connections across the various models, definitions, and criteria proposed for frailty. Some investigators have suggested all three – a model, a definition derived from the model, and explicit criteria for recognizing frail older persons.