Sidesystem

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A sidesystem is a separate group of headmates that exist, usually parallel/next to other systems within one larger plural body.

There may be a "main system" that most of the common fronters come from, or all sidesystems may function equally.

Related Terms
Sidesystems and subsystems describe similar phenomena, as both are different groups of headmates within one larger system. However, sidesystems usually don't exist within a headmate themself (like Russian nesting dolls) unlike many subsystems (although the latter can be used broadly).

Layers are also similar to sidesystems, and some systems may use them interchangeably.

Systems made up of subsystems and sidesystems can call themselves a polyplex.

Gallery
The dark blue represents the divisions between sidesystems, while the inverse color, the light brown, represents the opposite — connections between them. The dark brown represents the headmates within sidesystems.