A relationship in which fellatio is the ONLY sexual contact.
Harry goes to the club, where he happens to meet Sally. After a dance, Sally offers Harry fellatio in his car, which he accepts. Harry doesn't see Sally again, but he thinks they had a good fellationship.
Robert thinks Tricia is pretty darn skanky, but she's got some sexy lips and a stud on her tongue. He knows the only way to keep clean is for a fellationship.