Punch shots are usually played by somewhat more advanced players, as they are mainly about feel. Because they are about feel techniques probably vary a bit between individuals (just as do the names for the shot). But an easy way to think about it is that it is a partial shot (i.e., not a full swing). So, as an example, a common punch shot might begin with a backswing where the hands only reach shoulder-high and finish with the hands again shoulder high on the follow-through. It is also common to exaggerate the position of the hands forward (toward the target) to decrease the loft of the face a bit and keep the trajectory down.