Sibling System

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Sibling systems are when systems are in a sibling-like platonic relationship. This can be used by systems who are not bodily related but feel close like siblings, or systems who are close and bodily siblings. This term was created due to partner systems often having a romantic connotation (even though the definition is any type of close relationship).

Related Terms
This may be considered a specific, possibly familial, type of partner system.