A very very attractive girl who is a pure, hardcore, dyke lovin', never-in-a-million-years-would-touch-a-guy lesbian. She is considered a great loss in that no guy will ever have the pleasure of seeing what she can do between the sheets, hence the term lossbian.
*Note when two lossbians hook up, it is okay because the potential to witness hot girl on girl is there.
Guy 1: Dude, that chick is a solid 10! Whatta rack!
Guy 2: Ya...cept she is in love with Wanda Dinkle (points to the typical "other" lesbian girl, complete with a mullet, upper lip stash and muscle shirt showing off her anchor tatoo)
Guy 1: Oh, such a lossbian
Guy 2: Yup (sips brew to try and make Wanda appear better so when they kiss, it looks somewhat hot)