The Jargon File (version 4.4.7, 29 Dec 2003):

FIXME
 imp.

    [common] A standard tag often put in C comments near a piece of code that
    needs work. The point of doing so is that a grep or a similar
    pattern-matching tool can find all such places quickly.


    /* FIXME: note this is common in GNU code. */

    Compare XXX.


The Free On-line Dictionary of Computing (30 December 2018):

FIXME

    A standard tag often put in comments near a
   piece of code that needs work.  The point of doing so is that
   a grep or a similar pattern-matching tool can find all such
   places quickly.  This is common in GNU code.  Compare XXX.

   [Jargon File]

   (2001-03-16)