A plum is a fruit of the subgenus Prunus of the genus Prunus. The subgenus is distinguished from other subgenera (peaches, cherries, bird cherries, etc.) in the shoots having a terminal bud and solitary side buds (not clustered), the flowers in groups of one to five together on short stems, and the fruit having a groove running down one side and a smooth stone (or pit).
Mature plum fruit may have a dusty-white coating that gives them a glaucous appearance. This is an epicuticular wax coating and is known as “wax bloom”. Dried plum fruits are called dried plums or prunes, although prunes are a distinct type of plum, and may have antedated the fruits now commonly known as plums. Plums are a diverse group of species. The commercially important plum trees are medium-sized, usually pruned to 5–6 metres height. The tree is of medium hardiness. Without pruning, the trees can reach 12 metres in height and spread across 10 metres.
Fruits are usually of medium size, between 1 to 3 inches in diameter, globose to oval. The flesh is firm and juicy. The fruit’s peel is smooth, with a natural waxy surface that adheres to the flesh. The plum is a drupe, meaning its fleshy fruit surrounds a single hard seed.