Video Games Encyclopedia

Rail shooter, also known as on-rails shooter, is a subgenre of shoot ’em up video game. Beginning with arcade games such as the 1985 Space Harrier, the gameplay locks the player character into a set path, only allowing for limited or no divergence from it, in a manner similar to a theme park dark ride, which is typically on train tracks. While moving on this path, players must aim and shoot enemies while dodging projectiles and avoiding damage.

Many rail shooters feature a flying protagonist or ship. Some take place while walking, running or driving. While rail shooters saw a resurgence on the Wii due to its Wii Remote control scheme, new games in the genre are considered a rarity in the modern day, although many games of other genres contain rail shooter segments.

Reference: Wikipedia