Mesosystem

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A mesosystem is a system (sisasystem to be specific) within a system/polyplex/magistien, hemisystem, or other sisasystem that's too large and/or separate to be a sidesystem, but too small and/or not-separate to be a hemisystem. Mesosystems may contain sidesystems, subsystems, sparsystems, or any other grouping. The term comes from the Ancient Greek adjective for "middle, between, amidst".

Related terms
As a type of sisasystem, the term mesosystem is related to other sisasystem terms. While most commonly within a hemisystem, subplex, or larger/more separate grouping, mesosystems can be anywhere in a system's structure.

Metaregna are similar to mesosystems, being groupings of sidesystems, but are decidedly a "looser" form or type of grouping.