undefined

adj

1. (not-comparable)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.”

2. (not-comparable)That does not have a meaning and is thus not assigned an interpretation.

   “The result of division by zero is undefined.”

noun

1. An undefined value.

   “[Option:] · [PDP11:] F [BSD:] · [XE 2.3:] [1] [XE 3.0:] · [SIII:] · [COFF:] · [meaning:] make undefineds global”

   “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.”

   “The Array object has these commonly-used properties: • .length: the number of items including undefineds.”