A Body of Knowledge (BOK or BoK) is the complete set of concepts, terms and activities that make up a professional domain, as defined by the relevant learned society or professional association. It is a type of knowledge representation by any knowledge organization. In the theory several definitions are given, for example:

• Body of Knowledge is: (1) "Structured knowledge that is used by members of a discipline to guide their practice or work.” (2) “The prescribed aggregation of knowledge in a particular area an individual is expected to have mastered to be considered or certified as a practitioner.” (BOK-def). Waite’s pragmatic view is also worth noting: “BOK is a stepping stone to unifying community” (Waite 2004). - Tuncer Ören (2005),
• A 'Body of Knowledge' (BOK) is a set of accepted and agreed upon standards and nomenclatures pertaining to a field or profession. - INFORMS, 2009
• A body of knowledge (BOK) is a set of knowledge within a profession or subject area which is generally agreed as both essential and generally known. - Gary R. Oliver, 2012

A body of knowledge is the accepted ontology for a specific domain. A BOK is more than simply a collection of terms; a professional reading list; a library; a website or a collection of websites; a description of professional functions; or even a collection of information.