An item of apparel (eg. underwear) designed for either warming &/or covering the entirety or majority of a woman's muff (vagina, pussy, beef curtains, etc.).
"Just remember girls, no muff jacket's in the hot tub".

"May I remove your muff jacket with my teeth?"

"Hey Bucky, is that new muff jacket adequately warming your vagina?"
by Muffjacket May 23, 2013
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