A walnut is tough to crack but just because it's hard-shelled doesn't mean it's a
nut. In reality, walnuts are classified as drupes! Fruits that have a
fleshy covering over a hard shell surrounding the seed, are called
drupes like coffee, mangoes and coconuts. Dry fruit that just have a
hard shell covering a seed inside are true nuts, like hazelnuts,
chestnuts and acorns.