The three-ring release is the system attaching the main canopy's risers to the harness. Three interlocking rings of decreasing size create a mechanical advantage so that a load of hundreds of pounds can be released with a light pull.
Leverage, not strength
Each ring acts as a lever against the next, dividing the force at every stage. By the time the load reaches the small loop and cable holding the system closed, it is a tiny fraction of the total — which is why releasing a fully loaded canopy takes very little effort.
Invented by Bill Booth in the 1970s, it replaced earlier release systems and is now near-universal on sport rigs.
Why it needs maintaining
Riser webbing can take a set if left packed in the same position for long periods, which affects how freely the rings move. Periodic inspection and maintenance of the assembly is part of normal rig care and something a rigger will advise on.
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.