Plum is a type of fruit that belongs to the genus Prunus, which also includes peaches and cherries. The plum tree produces small, round or oval fruits with a smooth skin and juicy flesh in various colors such as purple, green, yellow or red. Plums are sweet when ripe but can be tart when unripe. They are often used for jams, jellies, pies, cakes, and other desserts due to their rich flavor.