Source : Free On-Line Dictionary of Computing

Job Control Language
     
         (JCL) {IBM}'s supremely {rude}
        {script} language, used to control the execution of programs
        in IBM {OS/360}'s {batch} systems.  JCL has a very {fascist}
        {syntax}, and some versions will, for example, {barf} if two
        spaces appear where it expects one.
     
        Most programmers confronted with JCL simply copy a working
        file (or {card deck}), changing the file names.  Someone who
        actually understands and generates unique JCL is regarded with
        the mixed respect one gives to someone who memorises the phone
        book.  It is reported that hackers at IBM itself sometimes
        sing "Who's the breeder of the crud that mangles you and me?
        I-B-M, J-C-L, M-o-u-s-e" to the tune of the "Mickey Mouse
        Club" theme to express their opinion of the beast.
     
        As with {COBOL}, JCL is often used as an archetype of ugliness
        even by those who haven't experienced it.  However, no
        self-respecting {mainframe} {MVS} programmer would admit
        ignorance of JCL.
     
        See also {fear and loathing}.
     
        (1999-03-03)