A pilot chute is a small drag device that starts the deployment sequence. Released into the airflow, it catches air, and the drag it creates pulls the main canopy out of the container and into the airstream.
Why a small chute opens the big one
A packed main canopy will not simply fall out of a container at 120 mph — something has to pull it. The pilot chute provides that force: it inflates almost instantly and drags the deployment bag out behind it.
Sport rigs commonly use a hand-deployed pilot chute stowed in a pouch at the bottom of the container, thrown into clean air by the jumper. Student and reserve systems often use a spring-loaded pilot chute that launches when released.
Terms you will hear alongside it
A bridle is the webbing connecting the pilot chute to the deployment bag. Pilot chute hesitation describes a pilot chute that fails to catch clean air promptly, usually because it has been thrown into the burble behind the jumper.
These pages explain what things are so the language makes sense. They are not instruction and cannot substitute for it — skydiving is taught in person by rated instructors at a drop zone, and anything involving equipment handling or emergency procedures belongs there rather than on a web page.