The rim is the hard metal edge — hitting it directly is a fault. A pocket is a hit on the netting close to that edge: legal and unpredictable.
These two words settle more points at the net than any technique, and they are the most common source of argument in casual games. If the ball hits the frame, the rally is over. If it lands on the netting close to that edge, it kicks off in a barely predictable direction — completely legal, and a popular weapon. A roll-up, where the ball rolls over the net into the rim and comes back out, also counts as good. The catch almost everyone misses: none of that applies to the serve — a side pocket on serve is a fault. And the practical note: deliberately hunting pockets without slipping into a fault is a game of millimetres — a weapon at elite level, but a source of errors for everyone else. Aim for the gap between your two opponents instead.