Plain English Meaning

Small latches that grab and hold the landing gear in place once it has been pulled up into the airplane, so it stays tucked away until the pilot tells it to come back down.

Full Definition

Mechanical latches that hold the landing gear securely in the retracted (up) position inside the wheel wells after retraction. They prevent the gear from falling out of the wells under its own weight, vibration, or aerodynamic loads, and must be released before the gear can extend.

Context Anchor

Seen in retractable-gear airplanes, especially when discussing abnormal or emergency landing gear extension.

Derivation

Up' refers to the retracted position of the gear; 'lock' is a device. Together: a lock that holds the gear up. Knowing this makes it why releasing the is the first in any extension — the gear cannot fall free until those latches let go.