Bullet Time is generally used in action games as a character ability. It allows the player to slow down time in order to dodge bullets, evade enemies, or attack enemies without giving them time to react. However, since bullet time obviously gives the player an unfair advantage, its use is usually limited. Depending on the game, bullet time may be a privilege the player can only use sparingly, or it may be something that the player is encouraged to use frequently. For example, in most of F.E.A.R., the player has only a short time to use bullet time before it runs out, while other games, like Max Payne 2, give the player an abundance of bullet time that regenerates very quickly.
The term bullet time comes from the first Matrix movie, where the slow motion effect shots of bullets flying through the air were known as "bullet time" shots. After "The Matrix" came out, many video game developers tried to use this concept with various degrees of success. However many people feel that the concept is now over-used as a mechanic to make a relatively mediocre game seem more technically solid.