Someone who is unusually fat and short at the same time. It does not have anything to do with a dumpster or being dirty. It is very similar to a chode, a penis that is fatter than it is long. Many girls can be called dumpy even if they are just a little bit squat.
"I don't know what you were thinkin last night dude, that flooz was dumpy as hell. Were you blind - she was like 5'1" with a gut. She was pretty much Yoda."