undefined adjective 3noun 1forms 1 adjective3 •Lacking a definition or value.We slid into our office, past two women discussing the "X factor," an apparently undefined quality their firm felt they lacked. — 1992 •That does not have a logically sound meaning within a specific formal system and is thus not assigned an interpretation.The result of division by zero is undefined.Within the set of real numbers, the square root of a negative number is undefined. •That behaves unreliably due to dependence on an uninitialized value or inconsistently ported code.In C, relying on a variable's value right after a malloc call is undefined behvaior. noun1 •An undefined value.Every operation is defined completely either by delivering a value of some type depending only on the types of its operands or by causing some defined exception; there are no ‘undefineds’ in Ten15. — 1988 formsundefineds
