A threesome between a hetrosexual couple and a third-party, where the third-party only ever interacts with one member of the couple who is of the same sex.
Essentially giving one person in the
partnership a bisexual experience.
Named after the character Ross Geller from from the sit-com 'Friends', when Ross proudly proclaims to Joey, that he had a threesome with his wife and her freind. However after additional discussion realises it wasn't much of a threesome at all as he didn't get to touch
the other woman.