built-in

from WordNet (r) 3.0 (2006)

built-in
    adj 1: existing as an essential constituent or characteristic;
           "the Ptolemaic system with its built-in concept of
           periodicity"; "a constitutional inability to tell the
           truth" [syn: {built-in}, {constitutional}, {inbuilt},
           {inherent}, {integral}]

from The Free On-line Dictionary of Computing (8 July 2008)

built-in

   (Or "primitive") A built-in function or operator is one
   provided by the lowest level of a language implementation.
   This usually means it is not possible (or efficient) to
   express it in the language itself.  Typical examples are the
   basic arithmetic and {Boolean} operators (in {C} syntax: +, -,
   *, /, %, !, &&, ||), bit manipulation operators (~, &, |, ^)
   and I/O primitives.  Other common functions may be provided in
   libraries but are not built-in if they are written in the
   language being implemented.

   (1995-02-14)