undefined

1. not comparableLacking 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, Lia Matera, Prior Convictions, page 121

   Synonyms: indefinite

2. not comparablecomputingThat 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.

   1 more example

   Within the set of real numbers, the square root of a negative number is undefined.

3. not comparablecomputingThat 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.

plural undefineds

1. computingAn undefined value.

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

   2017, Neos. Thanh, “Arrays”, in JavaScript Programming, →ISBN, page 36

   2 more examples

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

   1987, J. E. Lapin, Portable C and UNIX System Programming (Prentice-Hall Software Series), Englewood Cliffs, N.J.: Prentice-Hall, Inc., →ISBN, page 72

   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, Pearl Brereton, editor, Software Engineering Environments, Chichester, West Sussex: Ellis Horwood Limited, →ISBN, page 230