An elevator is a primary flight control surface that controls movement about the lateral axis of an aircraft. This movement is referred to as "pitch". Most aircraft have two elevators, one of which is mounted on the trailing edge of each half of the horizontal stabilizer. When a manual or autopilot control input is made, the elevators move up or down as appropriate. In most installations, the elevators move symmetrically but, in some fly-by-wire controlled aircraft, they move differentially when required to meet the control input demands. Some aircraft types have provisions to "disconnect" the right and left elevators from one another in the event of a control surface jam while other types use different hydraulic systems to power the left and right elevator to ensure at least one surface is operational in the event of hydraulic system failure(s).
B727 Flight Control Surfaces. Source: Wikicommons. Origin: FAA(USA)
The elevators respond to a forward or aft movement of the control column or control stick. When the pilot moves the controls forward, the elevator surface is deflected downwards. This increases the camber of the horizontal stabilizer resulting in an increase in lift. The additional lift on the tail surface causes rotation around the lateral axis of the aircraft and results in a nose down change in aircraft attitude. The opposite occurs with an aft movement of the flight deck controls.