A group of people, all of whom have slept with all other members of the group at some point in time.
Sally has slept with Bob, Johnny, and Suzie.
Bob has slept with Johnny, Suzie and Sally.
Johnny has slept with Suzie, Sally, and Bob.
Suzie has slept with Sally, Bob, and Johnny.
They are all bonded for life as an Eskimo Tribe.