A Rocket Start (also called a Turbo Start or Boost Start) is a speed technique introduced in Super Mario Kart and featured in every Mario Kart game since. It allows players to burst out of the starting line with blazing high speed, gaining a head start over any racer that simply drives out of the starting line. Similar to Mini-Turbos, Rocket Starts all vary slightly from game to game. You must press the Acceleration button at different times during the Pre-race countdown. Super Mario Kart's version had to be prepped right after the first light, and Mario Kart 64 and Mario Kart: Super Circuit was the exact opposite, on the final light. Since Mario Kart DS, Rocket Starts can be performed by holding A right after the 2 on the countdown fades (2 in Mario Kart Wii or Y in Mario Kart 7).
The technique was given a name in the instruction manual for Mario Kart 64.
Performing the Rocket Start too early will result in the kart stalling, so proper timing is needed, or you can get a really bad result.
Depending on the difficulty level, a varying number of computer opponents will utilize the rocket start. On lower difficulties, very few computer opponents will utilize the rocket start, giving every racer that uses the rocket start a massive advantage over them. As the difficulty increases, more opponents will use it. On Mirror Mode, very few opponents will stall at or drive out of the starting line.