An oily, malodorous substance found in the folds and cracks of one's butt. Typically found after a hasty wipe and/or following a rigorous workout routine. Similar to butt cheese or duck butter. Could also be a prime ingredient in the making of truffle butter.
Noun: I itched my butt and retrieved a healthy dollop of Rump Grease.

Verb: My girlfriend Rump Greased my driveshaft. I had to take an immediate shower. It itched for a week.
by Doc184 March 8, 2016
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