Subsystem

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A subsystem is a system within a system; oftentimes, when an individual member has a system of their own.

This can also refer to independent groups within a larger collective (although this is more commonly described as a layer or sidesystem).

Subsystems can experience any form of plurality as well.

Related Terms
Subsystem can function as an umbrella of sorts for subgroups within a system, including the terms listed above. Quite a few subsystems are median in nature, creating terms like ringed subsystem.