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A term often used by males to describe their relationship with a girl who is not their girlfriend, but a close friend. This term does not apply to blood-relatives.

This classification boasts qualities typically seen in brother/sister relationships (e.g., mildly derogatory dialogue, occasional use of derogatory hand gestures, random story telling and re-telling, matchmaking, inside jokes, mutual-aid and support related to interference by outside parties, and the occasional transfer of funds with no repayment plan).
Person 1: "Did you see how fat so-in-so has gotten?"
Person 2: "Hey, watch your face, that's my fake sister you're talking about."

Person 1: "So-in-so said you loaned her $200"
Person 2: "Yeah, it's ok. She's my fake sister. I'll hit her up for $400 next time."
by wordalicious December 07, 2010
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