A girl who claims to be lesbian, but really is not. This is claim is usually made due to several factors, sometimes all combined. Those being, Confusion, Aiming for acceptance from actual lesbians or other facebook lesbians, sometimes these girls have never fully matured and been able to open up and be comfortable around guys, so they just settle for girls who they are more comfortable with, especially with showing their bodies off.
Essentially a Poser.
Dude 1: Dint that chick just suck your dick last week? facebook says shes a lesbian..
Dude 2: Shes just a facebook lesbian man, shes a trendy homosexual.