Survival mode is a video game mode in which the player must continue playing for as long as possible in an uninterrupted session while the game presents them with increasingly difficult waves of challenges. A variant of the mode requires that the player last for a certain finite amount of time, after which victory is achieved and the mode ends. The mode is particularly common among tower defense games, where the player must improve the defenses of a specific location in order to repel enemy forces for as long as possible. Survival mode has been compared to the gameplay of classic arcade games, where players face off against increasingly stronger waves of enemies. This mode was intended to give the game a definite and sometimes sudden ending, so that other players could then play the arcade game as well.