The DICT Development Group

  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]

  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)