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

file descriptor leak
fd leak

    (Or "fd leak" /F D leek/) A kind of programming
   bug analogous to a core leak, in which a program fails to
   close file descriptors ("fd"s) after file operations are
   completed, and thus eventually runs out of them.

   See leak.

   (1994-11-30)