In turn-based or real time strategy games
In some circles it is also known as "zerging" or "Zerg Rushing" in reference to the Starcraft race. Most rushes are done early in a match. The goal of a rush is to catch an opponent with their pants down before they have built up adequate defenses. A properly orchestrated rush may see a match ending just a few minutes after it began. If the rush fails, the rusher often end up at a heavy disadvantage, thus it is one of the riskier strategies in most RTS games. The term entered into general internet lexicon after the popularity of Starcraft took off. One of its races, Zerg, is particularly well suited to rushing with its fast, inexpensive Zerglings, although any race is capable of it.
It is commonly held that the first "rush-able" game was the second game in Westwood's legendary series, Command and Conquer: Red Alert, which is also the first game to feature online play. It involved using the soviet faction to build multiple heavy tanks, which through their increased damage over their allied counterparts, the medium tank, basically made the allied player stand no chance. However, to counter this, the Allied player had a unit which the soviets did not, the rocket trooper, which, in enough numbers, could counter the tank rush. If the Allied player could survive the tank rush, the soviets are left with a massive disadvantage, having expended their resources, and unless the player is very skilled, it's their loss. This is also the first time a rush became a common strategy, because as statistics proved, the top Red Alert players were soviet, however, this could be because the soviets also required less overall skill than the allies for effectiveness. In Command and Conquer: Red Alert 3, a popular strategy is to create a sleuth of attack bears and send them into enemy territory to do as much damage as they can.
The strategy is as old as strategy gaming, and Starcraft wasn't even the first prominent game where its use became commonplace. Total Annihilation, which predates Starcraft by a year, had another notorious rush technique. In it, each player starts with a "commander" unit that is capable of building your first buildings, and also happens to be equipped with a nuclear warhead that detonates upon his death. This was often exploited within the first minutes of a match to devastating effect.