Qu'est-ce qu'un plum? Qu'est-ce qu'un plum? Any of several shrubs or small trees of the genus Prunus, bearing smooth-skinned, fleshy, edible fruit with a single hard-shelled stone that encloses the seed.The fruit of any of these trees.Any of several trees bearing plumlike fruit.The fruit of such a tree.A raisin, when added to a pudding or cake.A sugarplum.A dark purple to deep reddish purple.An especially desirable position, assignment, or reward: an ambassadorship granted as a political plum. Variant of plumb.Variant of plumb.