The control surface on an aircraft responsible for pitch control, usually located at the
rear of (or integral to) the tailplane.
Lowering the elevator increases the lift of the tailplane (at the rear of the aircraft), thus
pitching the aircraft's nose down; vice-versa for raising the elevators. They are connected to the front/back
axis of the control column.
Pulling back makes the nose go up, angle of attack increases and so does lift, until you stall.
The extra lift causes the aircraft to climb, thus trading kinetic energy for potential energy and
slowing down. If you are to continue the climb, energy must be added from an engine or other source,
otherwise the airspeed will rapidly drop below the stall speed for your current angle of attack.
An all-flying tailplane is one where the whole tailplane pivots to give an elevator effect. This
has the benefit of reduced drag but requires greater complexity and strength in that part of the aircraft,
increasing weight; it would also tend to interfere with the rudder unless placed significantly forward
or used in a T-tail configuration. The F-111 has an all-flying tailplane.
Conversely, pushing forwards reduces the angle of attack, reduces lift and you gain airspeed in a
dive.
Aircraft are often "trimmed" by adjusting a trim tab in the elevator. Moving the trim lever/wheel
(a sticky control like throttles that stays where you leave it) pushes the tab up and down, allowing the
aircraft to be set to a particular attitude. The trim tab behaves just like a mini elevator. Other
aircraft (without tabs) use a spring bias on the elevator so that some amount of force is applied without
any force on the control column; it achieves the same effect as a trim tab.