n. refers, denoting in its first sense the top portion of such a muffin, or sometimes a muffin cooked in a special shallow tin so that it consists exclusively of this top part, without the soggy bottom whose relative undesirability once inspired an episode of Seinfeld. The second sense is figurative, referring to a protuberance of flesh above the waistband of a tight pair of trousers (cf. spare tyre n., love handlen.), which may sometimes be attributed to an excessive appreciation for muffin tops in the literal sense.
Also added: OMG, LOL, FYI and Wag.