Video Games Encyclopedia

Shooter video games, or shooters, are a subgenre of action video games where the focus is on the defeat of the character’s enemies using ranged weapons given to the player. Usually these weapons are firearms or some other long-range weapons, and can be used in combination with other tools such as grenades for indirect offense, armor for additional defense, or accessories such as telescopic sights to modify the behavior of the weapons. A common resource found in many shooter games is ammunition, armor or health, or upgrades which augment the player character’s weapons.
Shooter games test the player’s spatial awareness, reflexes, and speed in both isolated single player or networked multiplayer environments. Shooter games encompass many subgenres that have the commonality of focusing on the actions of the avatar engaging in combat with a weapon against both code-driven NPC enemies or other avatars controlled by other players.

Reference: Wikipedia