(1) An IMS in a multisystem environment that accepts transactions from the front-end system, calls application programs for transaction processing, and routes replies back to the front-end system for response to the terminal. A back-end system may also perform front-end processing. A back-end system can be another IMS connected by an MSC link or can be part of the same IMSplex as the front-end system. See also front-end system.
(2) The CICS or IMS system in which existing applications run. Equivalent to partner system. See also front-end system.