A transsexual woman (born male and transitions completely to female) who is a lesbian and is also willing to date other tgirls.
Example 1: "No one can love you like one of your sisters" - a transbian
Guy #1: Dude, look at those chicks. They're frenching right in front of us!
Guy #2: Dude!
Guy #1: Wait... dude, I think they're dudes!
Girl: We're transbians. Get it right!
Guy #1: Woah... hawt.