A walnut is the edible seed of any tree of the genus Juglans (family Juglandaceae), particularly the Persian or English walnut, Juglans regia. The fruits of trees in the family Juglandaceae are often confused with drupes. Still, they are accessory fruit because the outer covering of the fruit is technically an involucre and thus not morphologically part of the carpel; this means it cannot be a drupe but is instead a drupe-like nut.

After full ripening, the shell is discarded, and the kernel is eaten. Nuts of the eastern black walnut (Juglans nigra) and butternuts (Juglans cinerea) are less commonly consumed.