The tight position just before release: disc close to the chest, elbow leading as the lever. This is where the disc gets its speed, not from an extended arm.
The power pocket is where your throw decides between speed and mere effort. The pull does not swing in an arc around your body, it travels past your chest as if on a rail: the disc stays close, the elbow leads as the lever, and only then does the arm extend. Its opposite is called rounding — the arm drifting around the outside of the body. That feels powerful, but it lengthens the radius and costs precision and distance instead of adding any. So train the tight pull line slowly, from a standstill and with a light disc, before you add a run-up. And here is what almost everyone misses: the power pocket is not a position you consciously hit, it is the result of a clean sequence from legs through hips to torso. Force it with the arm and you land in the overuse that catches most disc golfers' throwing arms anyway.