In video games, a level is any space available to the player during the course of completion of an objective. Video game levels generally have progressively increasing difficulty to appeal to players with different skill levels. Each level may present new concepts and challenges to keep a player's interest high.

Shoot 'em ups are a sub-genre of action games. There is no consensus as to which design elements compose a shoot 'em up; some restrict the definition to games featuring spacecraft and certain types of character movement, while others allow a broader definition including characters on foot and a variety of perspectives.