A glider is an aircraft that flies without an engine, soaring through the air by riding on currents of rising warm air called thermals. Unlike airplanes that use engines to stay aloft, gliders depend entirely on the shape of their long, slender wings and the pilot's skill at finding and using natural air movements.

Gliders start their flights by being towed into the sky by a powered airplane or launched with a winch, like a giant rubber band pulling a toy plane. Once high enough, the glider releases from the tow and begins its silent flight. Skilled glider pilots can stay airborne for hours, traveling hundreds of miles by spiraling upward in thermals, then gliding forward to find the next one.

The word can also refer to someone or something that glides smoothly. A hang glider is a simpler flying device where a person hangs beneath a large wing. Some animals are called gliders too: sugar gliders are small marsupials with flaps of skin that let them glide between trees, and flying squirrels use similar adaptations.

In furniture, a glider is a type of chair that slides smoothly back and forth on a fixed track instead of rocking on curved runners.