Definition
Speedbrakes are aerodynamic devices, usually deployable panels on the wings or fuselage, designed to increase drag without significantly changing the lift the airplane is producing. They allow the pilot to slow the airplane or increase the rate of descent without reducing engine power.
Plain English
Speedbrakes are flat panels the pilot can extend into the airflow to make the airplane slow down or come down faster, without having to pull the throttle back.
Context Anchor
You may see this term in stall recovery guidance, descent planning, and aircraft operating procedures for airplanes equipped with these panels.
Derivation
From 'speed' + 'brake' -- literally a brake for speed. The name describes exactly what the device does: it brakes (slows) the airplane through the air, in contrast to wheel brakes which slow it on the ground.
Why Pilots Care
Allows rapid reduction of airspeed during stall recovery or other situations where excess speed must be dissipated without large pitch changes.
Intuition Check
Speedbrakes do not work like wheel brakes. They do not grab a wheel; they create extra air resistance while the airplane is moving through the air.
Example Sentence 1
After leveling off above the cloud layer, the pilot extended the speedbrakes to slow the airplane below maneuvering speed.
Example Sentence 2
In a steep descent the crew deployed the speedbrakes to keep airspeed below the red line.