A gold star lesbian is a lesbian that has never had sexual intercourse with a male. The term refers specifically to penetrative penis/vagina intercourse between a man and a woman, and does not refer to transgendered men.
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Of course, many homosexual females experiment with sex with men as well as women during their journey in determining their sexuality. Thus, the gold star ranking separates those who have never "experimented" with the opposite sex when it comes to sexual intercourse.
