(Namespace: plural glossary)

When two or more people are headmates, it means they are different people—for any meaning and extent of the words “different” and “people”—who live in the same body and would appear to outside observers to be the same person.

A headmate may come from a source and/or perform a role within the system. Headmates are sometimes aware of each other, and sometimes not.

(A headmate is that same sort of entity which, among outsiders to the plural community, is variously referred to as an alter ego, alternate identity, split personality, or imaginary friend. These are generally not preferred terms; all of them are either glorifying, stigmatizing, or minimizing, and some of them apply only to specific types of headmates but are wrongly generalized to all of them. I include them here only to more clearly convey the overall concept to the uninitiated.)