A sugar plum originated as a piece of dragée or hard candy made of hardened sugar in a small round or oval shape.
"Plum" in the name of this confection does not always mean plum in the sense of the fruit of the same name, but commonly refers to small size and spherical or oval shape. Traditional sugar plums often contained no fruit, but were instead hardened sugar balls. These hardened sugar balls were comfits, and often surrounded a seed, nut, or spice.