Definition
Ailerons mounted on the outer portion of each wing that are active only at low airspeeds, used to provide roll control during takeoff, approach, and landing on large swept-wing jet aircraft. At higher airspeeds these surfaces are locked out, and roll control is handed over to inboard ailerons and roll spoilers to prevent excessive wing twist (aileron reversal) that the long, flexible outer wing could otherwise produce.
Plain English
These are the roll-control surfaces near the wingtips that only work when the aircraft is flying slowly. At high speeds they are switched off, because using them out near the wingtip would flex the wing and could actually roll the aircraft the wrong way.
Context Anchor
Seen in discussions of high-speed flight controls, especially on larger or faster airplanes that use different roll-control surfaces at low speed and high speed.
Derivation
"Outboard" means farther from the centerline of the aircraft, so these are the ailerons mounted near the wingtips. The pairing with "low-speed" flags that they are only used in one part of the flight envelope.
Why Pilots Care
Locking these surfaces at high speed reduces wing twisting forces that could otherwise cause structural fatigue or control reversal.
Intuition Check
Outboard does not mean “outside the airplane”; it means farther from the airplane’s centerline, toward the wing tip. Low-speed does not mean the aileron is slow to move; it means the aileron is intended for use in the slower-speed part of flight.
Example Sentence 1
On takeoff and approach, the outboard low-speed ailerons assist the inboard ailerons to give crisp roll response when the aircraft is flying slowly.
Example Sentence 2
Once the aircraft accelerated past 250 knots the outboard low-speed ailerons locked so the inboard surfaces and spoilers handled roll inputs.