A "shmup" is a sub-genre of action games, short for "shoot em up". In a shmup game, the player controls a single entity, usually a spacecraft, and combats a large number of enemies by shooting at them while dodging their fire. The player must rely primarily on reaction times to succeed. Critics differ on exactly which design elements constitute a shoot em up, but some restrict the genre to games featuring some kind of craft, using fixed or scrolling movement. The term "shmup" is believed to have been coined in 1985 by the British Commodore 64 magazine Zzap!64. Shmups are often associated with classic 2D arcade games of the 1980s. Some examples of shmup games include Gradius, Thunder Force IV, R-Type, DoDonPachi, Ikaruga, and Raiden.