What fruit is actually a nut, and how is it different from other fruits in terms of classification and characteristics?

The fruit that is actually a nut is the coconut. Coconuts are different from other fruits because they have a hard, woody shell and are classified as a drupe rather than a true nut. Drupes have a fleshy outer layer surrounding a hard shell with a seed inside, while true nuts have a hard outer shell that does not split open on its own.