Horizontal Stabilizer: Horizontal Stabilizer
Elevator: Elevator
Stabilator: Stabilator
Anti-Servo Tab: Anti-Servo Tab

The Elevator is typically installed at the rear section of the Horizontal Stabilizer. The Horizontal Stabilizer is fixed, while the Elevator is movable.

However, for a Stabilator, the stabilator itself functions as the elevator.
Trim is still necessary, and this is often achieved by the movable section at the rear of the Stabilator
—the Anti-Servo Tab.

<img src=http://image.slidesharecdn.com/aircraftbasics-140927035356-phpapp02/95/aircraft-basics-35-638.jpg?cb=1411790115>

But perhaps more importantly,
the Anti-Servo Tab provides the pilot with tactile feedback during control inputs,
ultimately helping to prevent over control.

For example, when the pilot pushes the stick forward, the Stabilator tilts upward,
increasing the angle of attack of the horizontal tail, generating more Lift at the rear of the aircraft, and causing the nose to pitch down (nose down).
However, the effectiveness of the elevator is often very pronounced, resulting in very light control forces.
Without an Anti-Servo Tab, there would be insufficient force feedback,
and the pilot might overcontrol.

With an Anti-Servo Tab,

using the example of pushing the stick forward (lower part of the image above),
the movable section of the Anti-Servo Tab moves more than the stabilator itself.
Therefore, for the Stabilator, considering the lever action,
it creates an opposing force on the control stick.

Thus, the pilot can clearly feel the resistance when pushing the stick,
resulting in better control feel,
and achieving the effect of preventing over control.