Easy. Once you get placed in the "friend zone", you ain't gettin' the pussy... so she's a girl friend. You'll be the boy friend she'll call when she breaks up with her boyfriend.
A girlfriend you've kissed, fucked, or whatever but have an ongoing relationship that focuses on love and development. A girl thats a friend is a friend. Simple to me. I have friends with benefits but they are friends. Great friends usually, but not girlfriends. I prefer FWBs than girlfriends.