The logic behind the word’s analogy is that, in both cases, an overflowing object is partially constrained by a vessel. The sharp pressure differential at the vessel’s opening allows the contents to spill over creating the familiar ‘Muffin Top’.
This word originated as Australian slang in mid-2003, but has since become popular in other English-speaking countries.
Australia’s Macquarie Dictionary named this as the word of the year in 2006;
The American Dialect Society named it one of the “most creative” new terms that same year. The Oxford English Dictionary added the term to its revised online edition in March 2011.