A bitch. Someone who constantly steals other people's boyfriends. She plays games, talks shit behind your back and lies to you constantly. This kind of girl will never really love or commit to you. She cheats on every boyfriend she ever has, and usually has a full time boyfriend on the side...sometimes even a girlfriend.
"Dude, that Emily totally slept with my boyfriend."
Guy - "She cheated on me."
Friend - "What an Emily move, man."