Pinching is a technique of pruning a bonsai tree that involves removing the tips of new shoots with the fingers. Pinching helps to shape the bonsai and maintain its miniature size. Pinching also encourages the development of smaller leaves and branches, which enhance the aesthetic appeal of the bonsai. Pinching should be done regularly and carefully, as over-pinching can weaken the tree and reduce its vigor. Pinching should also be done according to the type and season of the bonsai, as different species have different growth patterns and needs.