Source : Free On-Line Dictionary of Computing

zombie 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)