People who are sexually intimate with when they are both between relationships - similar to friends with benefits, but with the expectation that while the friendship will continue, the benefits are put aside when one of the people involved gets involved in a romantic relationship.
TWEENER (n.) - a dyke who has feminine features, mannerisms, proclivities, etc., but cuts her hair short and dresses butch in order to secure her lesbian identity. Connotations: the look does not suit her; she is insecure
She's just come out, so I think she's going through a tweener phase. She keeps buying Dickies and a-shirts, but talking about how she misses high heels.