Meaning – The term job entry subsystem, refers to the IBM licensed program that receives jobs into the system and processes all output data produced by the jobs.
JES is the component of the operating system that provides supplementary job management, data management, and task management functions such as scheduling, control of job flow, and the reading and writing of input and output streams on auxiliary storage devices, concurrently with job execution.
z/OS manages work as tasks and subtasks. Both transactions and batch jobs are associated with an internal task queue that is managed on a priority basis. JES is a component of z/OS that works on the front end of program execution to prepare work to be executed.
Example of usage – “JES is also active on the back end of program execution to help clean up after work is performed. This activity includes managing the printing of output generated by active programs.”