Job Control Language
Abbreviated as JCL, Job Control Language is a means of communicating with the IBM 3090 MVS Operating System. JCL statements provide information that the operating system needs to execute a job. A job is something that you want to accomplish with the aid of a mainframe computer (e.g. copy a data set, execute a program, or process multiple job steps). You need to supply the information that the job requires and instruct the computer what to do with this information. You do this with JCL statements. A job step consists of statements that control the execution of a program or procedure, request resources, and define input and/or output.
[Source: Job Control Language (JCL) Introduction]