The, in fact, unenjoyable fat that hangs over the way too tight pants of a hefty lady. Therefore, giving a relation to the top of a muffin. Also possible to be a noun, example below. (A.K.A. Jessica)
"WHOA, don't look now, it's Muffin-tops in Spandex, why does she put herself and everyone else in harms way wearing stuff like that?!"