A friendly male bonding gesture in which a man thrusts his penis into another man's anus. Similar to brofist, only more meaningful and significant, usually reserved for occasions where a man has done something especially great or awesome enough to warrant a bropump.
Dave: Hey bro, I was at Best Buy today and got you a copy of Battlefield: Bad Company 3 so that you and I can play together. I know money is tight for you right now, but hopefully this will bring you some enjoyment.
Steve: Holy shit, bro!! You serious?! Thanks a lot, that's awesome!! Brofist! No... wait... this calls for something greater. Get over here and unzip your pants real quick!
Dave: Um, what?
Steve: Bropump, man, bropump!! Hell yeah! Hurry up, while I'm still hard.
Dave: Uh, Steve, doesn't that seem kinda gay to you?
Steve: Nah bro nah, not gay at all, just showing you some appreciation. I'm straight, you're straight. I've done this plenty of times with my other bros.