Sisasystem

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A sisasystem is an umbrella term for systems that are smaller in population than the body they inhabit, or smaller in size than all innerworlds connected to that body. Examples of sisasystems include (nested) subsystems, sidesystems, hemisystems, and sparsystems. This can also be used as a general term when such a group doesn’t fit into the subsystem/sparsystem/sidesystem/hemisystem model, chooses not to classify itself with that model, or is unclassifiable (at least not easily classifiable) by those systems for any other reason. Comes from Finnish “sisällä”, meaning “inner, internal, interior”.

Related Terms
Subsystems, sparsystems, sidesystems, mesosystems, hemisystems, subplexes, sideplexes, mesoplex, and hemiplexes are all varieties of sisasystem, in ascending order from stereotypically least-separate/smallest to most-separate/largest. However this is a very loosely defined hierarchy, and it is ultimately completely up to the system in question to decide which terms to use for themselves and groupings within their own system, additional or replacement terms can be used, and the terms don't have to be used at all.

Layer clusters/metalarachs, metaregna, pasáuliai, and various types of sisasystem clusters (a term which includes the last two, but not layer clusters) are similar terms, but fundamentally different in that they are much looser or more informal/formalized groupings rather than structural groupings.