Strictly speaking, a dump such that all the excrement would fill up 1,000,000 Standard high capacity Canadian toilets. (mega is the SI suffix for a million.) colloquially, it is a massive crap such that the defecator feels like he has just dropped the Fat Boy. Mofos with irritable bowel syndrome are notorious for releasing these and then bragging to their friends that they feel about 10 pounds lighter.
Craig: You took another megadump, didn't you? Now no ones going to be able to use it until the janitor gets it unclogged manually.
Bob: it wasn't me.... Uh... It was the guy before!
Bob: it wasn't me.... Uh... It was the guy before!
by Craptastic16 October 19, 2012