Plain English Meaning
Wheels that tuck up into the airplane after takeoff so they don't slow it down, and come back out before landing.
Full Definition
A landing gear system that folds or pulls up into the structure of the airplane after takeoff and extends back out for landing. Retracting the gear in flight reduces aerodynamic drag and improves cruise performance. The system is typically operated hydraulically, electrically, or by a combination of both, and includes position indicators and a backup method for lowering the gear if the normal system fails.
Derivation
From the Latin retrahere, meaning 'to draw back.' The gear is literally drawn back into the airplane after takeoff.
Why Pilots Care
Reduces drag for higher cruise speeds and better fuel economy, yet requires precise operation during takeoff and landing to avoid damage or gear-up incidents.
Intuition Check
Retractable does not mean the gear disappears or is removed. It means the gear is pulled into the aircraft for flight and extended again for landing.
Example Sentence 1
After a positive rate of climb, the pilot raised the retractable landing gear to reduce drag.
Example Sentence 2
On the before-landing checklist the student confirmed the retractable landing gear was down and locked.