Plain English Meaning
Latches that hold the landing gear firmly in place once it has finished moving — one set holds the gear up after takeoff, another set holds it down for landing.
Full Definition
Mechanical devices on a retractable landing gear system that physically secure each gear leg in either the fully retracted (up) position or the fully extended (down) position. The uplock holds the gear up against the airflow and gravity after retraction, while the downlock holds the gear rigidly in place when extended so it can support the airplane's weight on landing.
Context Anchor
Seen during preflight inspection of airplanes with retractable landing gear, especially when checking the gear, doors, linkages, and visible locking parts for damage or security.