When people of either gender pretend to be the opposite sex in a chat room. This is most common with men as they pretend to be so called "girls". I don't see why a girl would pretend to be a guy, but it's possible. It's relatively easy to identify a chat tranny. Annoying them or blowing thier cover will cause them to type the way thier real gender does. Be on the look out for them in chat rooms.
chat tranny: "Anyone wanna chat with a sexxy girl?"
chatter: "No piss off and stop being a chat tranny."
chat tranny: "Oh you son of a b****! I'm gonna kick your a**!"