Stone fruits (or stonefruits or stonefruit), in botany, refers to drupe, fruits in which an outer fleshy part (exocarp, or skin; and mesocarp, or flesh) surrounds a shell (the pit or stone) of hardened endocarp with a seed inside. These fruits develop from a single carpel, and mostly from flowers with superior ovaries. The definitive characteristic of a drupe is that the hard, lignified stone (or pit) is derived from the ovary wall of the flower.
More specifically, "stone fruit" refers to members of the genus Prunus, which includes plums, cherries, mangos, peaches, apricots and almonds. It is traditionally placed within the rose family Rosaceae as a subfamily, the Prunoideae (or Amygdaloideae), but sometimes placed in its own family, the Prunaceae (or Amygdalaceae).
The term is sometimes used in supermarkets to categorise peaches, nectarines, plums, etc.