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

zombie process
defunct process

    (Or "defunct process") A Unix process
   that has terminated (either because it has been killed by a
   signal or because it has called exit()) and whose parent
   process has not yet received notification of its termination
   by executing (some form of) the wait() system call.

   A zombie process exists solely as a process table entry and
   consumes no other resources.  This entry is retained to hold
   the child's exit status until the parent process wants to
   retrieve it.  The parent can also be notified asynchronously
   via a signal of the child's termination.

   Zombie processes can be seen in "ps" listings occasionally
   (with a status "Z" in some versions).

   Compare orphan process.

   (1997-10-08)