Definitions are considered in terms of various purposes as well as lexical and stipulative definitional types. Methods of stipulative definition that have been tangled together in gang research and theory are identified as analytic definition and synthetic definition, with the latter including correlational, causal, and definition by description. The article examines how various researchers and theorists have fallen into various errors of logic in use of these methods and how gang research and theory might make more consistent progress through clarification of the definitional issues. The article includes sections concerning: (1) Methods of Lexical Definition; (2) Methods of Stipulative Definition; (3) The Implicative Method; (4) The Denotative Method; (5) Definition by Analysis; (6) Synthetic Definition; (7) Correlational Synthetic Definitions; (8) Causal Synthetic Definitions; and (9) Synthetic Definitions by Description. References