(1) In DB2 for z/OS, a distinct instance of a relational database management system (RDBMS).
(2) An operating environment, defined by a subsystem description, where the system coordinates processing and resources.
(3) A secondary or subordinate system, usually capable of operating independently of, or asynchronously with, a controlling system.
(4) In z/OS, a service provider that performs one or many functions, but does nothing until asked. For example, each WebSphere MQ for z/OS queue manager is a z/OS subsystem.
(5) In the Remote System Explorer, a container for a particular user's remote System i libraries, command sets, and jobs.
(6) A model element that has the semantics of a package, such that it can contain other model elements, and a class, such that it has behavior. The behavior of the subsystem is provided by classes or other subsystems it contains. A subsystem realizes one or more interfaces, which define the behavior it can perform.
(7) In Unified Modeling Language (UML), a grouping of model elements, of which some constitute a specification of the behavior offered by the other contained model elements.