Cover system

A cover system is a video game gameplay mechanic that allows a virtual avatar to hide from and avoid dangers, usually in a three-dimensional world. This method is a digital adaptation of the real-life military tactic of taking cover behind obstacles, for purposes of attaining protection from enemy ranged or area effect attacks, such as gunfire or explosions. Similar gameplay elements can be traced back to as early as 1986, in Rolling Thunder. Later games which refined the system include Bonanza Bros., Blackthorne, Time Crisis, Metal Gear Solid, WinBack, Police 911, Splinter Cell, Kill Switch, Gears of War, Uncharted, Mass Effect and Vanquish.

In gaming, a cover system lets a player character use stationary or moving obstacles to avoid damage. To be considered a cover system, there must be some physical interaction with the source of cover and the avatar. This means standing behind an object, as in traditional shooter games, while strictly speaking would be classified as taking cover, does not qualify as an actual cover system. Some first-person shooters such as Soldier of Fortune bridged the gap somewhat by allowing players to lean to the sides, allowing the avatar to lean out from behind objects to survey the environment or open fire on the enemy, without fully moving their own bodies into the open. In addition, the player character must have the ability to move in and out of the covering objects' proximity, leaving points of vulnerability to the player. This excludes the exclusive use of portable shields as a cover system, though they may often be used to supplement a stationary source of cover, as seen in video games like Army of Two, and Gears of War 2.

...
Wikipedia