My American chestnut ancestors produced heavy crops of nuts annually. From left to right, the nuts in the photo are the American, Chinese, Japanese, and European chestnut. Mouse-over to see which nut is me.
A nut is the fruit of some trees. Each nut is a single seed inside a hard shell. Chestnuts are covered by a protective coat called a bur. The oak tree's acorn is an example of a nut that is only partially covered by a bur. We call this the acorn's cap.