Sisasystem

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A sisasystem is an umbrella term for formalized groups within systems, such as 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 of terminology for any other reason. Comes from Finnish “sisällä”, meaning “inner, internal, interior”.

Related Terms
Subsystems, sparsystems, sidesystems, mesosystems, hemisystems, subplexes, sparplexes, sideplexes, mesoplexes, and hemiplexes are all varieties of sisasystem, in ascending order from smallest to 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, lavhachruks, 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/nominal groupings rather than structural or more formal ones.