Over-the-shoulder, as its name suggests, is a camera mode where, during gameplay, the camera sticks behind the player character at all times, showing the world from a viewpoint behind and above the character's shoulders, usually not showing further down than the hips; as opposed to more traditional third-person-shooter approaches of either having the character control entirely separate from the camera or having the character's entire body on-screen, facing in the direction of the camera.
Over-the-shoulder aiming was first brought to prominence by its use in Capcom's Resident Evil 4, which first demonstrated this perspective at E3 2003, but was delayed and re-worked, eventually releasing in 2005 to considerable acclaim. The concept was later relied on heavily in 2006's Gears of War, which led to even greater attention and adaptation. It has since become the de facto standard perspective of third-person action games. This viewpoint is often used along with a laser sight mechanic.