(1) A called program that is combined with the calling program at run time to produce a run unit. A subprogram is below the calling program in the call stack.
(2) A program that is called by another program, such as a subshell. See also main program.
(3) In FORTRAN, a program unit that has a FUNCTION, SUBROUTINE, or BLOCK DATA statement as its first statement.
(4) In the IPA Link version of the Inline Report listing section, an equivalent term for 'function'.