Definition
A flight control system in which the pilot's physical input on the yoke, stick, or rudder pedals is assisted by a hydraulic or electric power source, but the pilot still moves the control surfaces directly through mechanical linkages. The power assist reduces the effort required, while the pilot remains in primary control of the surface.
Plain English
Flight controls that give the pilot a power-assisted helping hand, similar to power steering in a car. The pilot is still physically moving the controls, but a hydraulic or electric system makes it easier.
Context Anchor
Seen in discussions of flight control systems, especially on larger or faster aircraft where the air loads on the control surfaces can be too strong for manual force alone.
Derivation
Boosted' comes from the idea of giving something an extra push or lift. In this context, the pilot's effort is being boosted -- amplified -- by a power source, so smaller pilot input produces full control surface movement.
Why Pilots Care
On larger or faster aircraft, the air loads on control surfaces can be too heavy for a pilot to move by hand. Boosted controls make these aircraft flyable while still giving the pilot a direct mechanical connection to the surfaces, which matters for control feel and for what happens if the boost system fails.
Analogy
Think of power steering in a car. You're still turning the wheel and the wheel is still mechanically connected to the tires, but a hydraulic pump is doing most of the heavy lifting. Boosted flight controls work the same way.
Intuition Check
Boosted does not mean the airplane is controlling itself. It means the pilot’s control input is being helped by an added power source.
Example Sentence 1
On larger aircraft, boosted controls allow the pilot to move the ailerons and elevator without fighting the heavy aerodynamic loads at high speeds.
Example Sentence 2
On the high-speed jet the instructor demonstrated how boosted controls prevent control forces from becoming too heavy.