Sandbox

A sandbox is a type of video game level design that consists mainly of an open world environment that the player can roam freely, as well as non-linear gameplay. Although there is a large variety of sandbox games, the Grand Theft Auto series is considered as one of the most popular examples of this type of gameplay.

Game Design
From a design perspective this approach to game design the sandbox has two main traits: There is a third trait of sandbox games, in which the world is procedurally generated, meaning that each time a new game is started, a new map is made from scratch, using algorithms. This is not the case in the GTA series, therefore making it not a "true" sandbox game, even though it still fulfills most of the other criteria which would make it a sandbox game.
 * Non-linear gameplay: the player can choose how they like to play the game, such as the order in which missions are played, as long as it doesn't change the storyline.
 * Free-roam: The user can explore the game world as they like, free of any restrictions or constraints of any sort. Again, this is often manipulated to avoid discrepancies in the storyline (Like in GTA San Andreas, where the cities are unlocked as the player advances in the game's story).

Grand Theft Auto series
All Grand Theft Auto games are of a sandbox type. Grand Theft Auto III is considered as the most important sandbox game in video game history, as it was one of the first best-selling games to be of such a nature. This inspired other developers to make games of this kind, like Fallout. Although one of the most influential, the GTA games were not the first, nor the last, sandbox games. The series directly inspired a wave of games deemed as "GTA Clones" like Saints Row, True Crime and Driver.