I do know what it is, but I didn't run across it until I met Cass, who was born and raised in Chicago. I grew up in Maryland, myself.

When I was in college, I noticed at one point that Websters didn't know the derivation of the word, and it suggested that maybe it was onomatopoetic for the noise you made eating it. I spent several weeks trying to figure out how to write in to them and explain.