The Collaborative International Dictionary of English v.0.48:

job control language \job control language\ (Computers)
   A programming language used to specify the manner, timing,
   and other requirements of execution of a task or set of tasks
   submitted for execution, especially in background, on a
   multitasking computer; a programming language for controlling
   job[7] execution. Abbreviated JCL.
   [PJC]

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

Job Control Language
JCL

    (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)