Originally a mispronunciation of "Cream of Mushroom" soup, when it was prounounced "Queem of Mustard" by a waitress at The El Dorado Diner in Tarrytown, NY. It has no real meaning besides how funny it sounds.
There is an alternate spelling, "Queem of Muffturd," which is a conglomeration of many other words such as cream, queef, muff, and turd.
"Yes, I'll have the Queem of Mufftard in a bowl, please."
"Dude, my girlfriend totally busted out with some Queem of Muffturd last night in bed. It was disgusting; it took me hours to clean up."