A dyno, short for dynamic move, is a climbing move in which you spring off the wall to reach a hold too far away to grab statically. At full extension all four limbs may briefly leave the rock before your hands latch the target hold. It trades control for reach and is a signature move of modern bouldering.
Rappelling, also called abseiling, is the technique of descending a rope in a controlled way using friction from a belay or rappel device. Climbers use it to get down from routes and anchors. Because it depends entirely on the system being built correctly, rappelling is a leading cause of climbing accidents and demands rigorous checks.
Belaying is the technique of managing a climbing rope to protect a climber from falling. A belayer uses a belay device and the friction of the rope to hold a fall, lower the climber, and feed or take in slack as the climber moves. It is the core safety system of roped climbing.