Plain English Meaning
Aircraft without engines. They stay airborne by trading altitude for forward motion, or by riding rising columns of air, after being launched by a tow plane or winch.
Full Definition
Heavier-than-air aircraft that are not engine-driven and sustain flight through the dynamic reaction of the air against their lifting surfaces, using gravity, rising air currents, or a tow for propulsion and altitude.
Context Anchor
Seen in FAA discussions where equipment rules, operating limits, or aircraft categories may treat gliders differently from powered airplanes.