A term used to describe someone who is all out and willing to go completly crazy at something/someone. Term comes from COD act of running crazy around and inside everywhere, and just trying to get kills even though the opposite team might be in big groups/camping.

When your walking down the street, maybe with a friend. And you see a bum just sitting, standing, or laying down. You step back, take a deep breath, and sprint toward the bum at full speed. once close, you crossbody him in mid-air, once on the ground you beat the living fuck out of the bum. BUMRUSH.

When two or more people rush at something like a pair of bums rushing towards a piece of food, carboard box, soap, etc;

The sudden, unexpected urge to poo after taking the first few drags of a cigarette.

The act of sternly and viciously executing a surprise attack on someone or something's bum, possibly against their will and usually by a group, in pursuit of sexual pleasure on the part of the bummer(s).

a group of friends gather and yell BUM RUSH and gang up on a poor defensless person as a group of bums would do for money and without regard of the persons heath,spray him with different kinds body deoderant everywhere of his body until he/she is on the ground gasping for air.

The correct definition of the word is actually:

Bumrush orginated when homeless peoples would come into a store and start loitering and casuing disturbances looking for places to sleep/eat/take shelter. These are stores such as super markets or retail stores. Store managers, became disgusted and tired of the homeless and degenerate roaming through their stores in search of warmth and possible indulgence of a twinkie or two. They went into the back storage room and usually took a broom and then went on a frenzying rush to rid their stores of bums. Thus the store went back to it's original status of a respectable and pleasant place to shop.