LOL..its just one of those wonderful fun slang terms!
Per Wikipedia:
Vaginal flatulence (flatus vaginalis in Latin) is an emission or expulsion of air from the vagina, often during or after sexual intercourse or (less often) other sexual acts, stretching or exercise. The sound is somewhat comparable to flatulence from the anus but does not involve waste gases and thus often has no specific odor associated.
Slang
Queef (onomatopoeia), pussy fart, and vart are slang terms which refer to vaginal flatulence. The term fanny fart is also commonly used in Britain and Australia
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