Job Entry System - is a subsystem of an MVS (OS/390 or z/OS) mainframe operating system that accepts jobs (units of work) into the system and processes all output data produced by the jobs. Each job is defined by a user and executed according to the rules (or configuration) established by the system administrators. This includes the priority given to the job and the allocation of resources needed to perform the job. JCL (or Job Control Language) is usually used to define and run batch jobs. For additional information refer to the JCL definition in this glossary.