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In Britain, used to refer to the labia majora of the female vagina. Otherwise known as the vaginal "lips".

Can be used as a derogatory term, in the same way that cunt, dick, asshole would be used.
That chick has huge fanny flaps.

I'd like to wrap my fanny flaps around that guy's cock.

Shutup fanny flaps.
by Dave March 05, 2003
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