Binary System

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A binary system is a term for a system consisting of two members, not counting fragments or other non-realized or non-native headmates.

Related Terms
Diapathic is a close synonym for systems consisting of two members, and Duanumeren is a -numeren synonym to Diapathic.

Diplotic System refers to a system that has had two members since the beginning, but may or may not have gained more members since then.

History
The term was coined by The Bard Gang.

The term origin may be interpreted to be coming from astronomy.