Definition
A fat belly, as opposed to one with a six-pack. See definitions 1 and 2 of six-pack. Seldom used in the plural.
Origins
Likely by analogy with six pack of abs, the abs exchanged for rolls (“visible folds in the belly caused by obesity”).
How People Actually Use It
Six pack of jelly rolls is a term used to coin a person who's "abs" are really just rolls of fat.
"Girl: "Wow, check out Fabs's six pack!" Guy: "He's sucking in all his fat. Look, he's just got a six pack of jelly rolls!""
Source: Urban Dictionary