taking two shits in immediate succession of each other. taking yet another shit when you've just finished a shit. happens especially after a night of heavy drinking, when you've just finished a serious beer shit, the ass juice isn't yet evaporated, you're getting off the crapper and you realize you have to go again. can be used as verb or noun.
fuck me i got so locked last night at paddy's stag, i had to double dump this morning.
dude, it's been half an hour and still smells. that must have been some serious double dump you did.