Nut, a term commonly used for an edible or commercially useful seed covered with a hard shell. To botanists, a nut is a type of fruit that consists of one seed covered with a dry, hard shell that does not split when the fruit is mature. Acorns and hazelnuts are examples of true nuts.

Most so-called nuts are not nuts but other types of fruits. Walnuts, almonds, pecans, macadamia nuts, and coconuts are drupes, fruits similar to peaches and plums. While the fleshy parts of peaches and plums are the parts that are eaten, the fleshy part of walnuts, for instance, becomes a rough, dry husk that is removed in preparation for market. The shells of these drupe "nuts" correspond to the hard outer layer of peach stones; and the nut meats, to the almondlike seeds inside peach stones. Peanuts are legumes, related to peas. The shells are pods, and the peanuts are seeds. Litchi nuts are berrylike litchi fruits that have been dried whole.

Many nuts contain a nutritious food supply in their cotyledons or endosperm, the parts of a seed that feed the plant embryo before it is able to make its own food. Certain nuts are noted for their high percentage of oil (pecans, peanuts, Brazil nuts), protein (almonds), or carbohydrates (chestnuts).

Nuts are of great commercial importance in the United States. Peanuts, pecans, and walnuts are the largest food-nut crops; almonds and filberts are also valuable. Tung nuts and peanuts are grown for their oil. Peanuts and peanut plants are fed to livestock. Tropical nuts are used in a variety of ways. For example, coconuts are a source of fiber, and betelnuts and kola nuts are used as stimulants.

Nut trees are usually propagated by grafting part of a tree producing desirable nuts onto a hardy or disease-resistant stock. Seedlings are used only for root stock, developing new varieties, or improving old ones. Some nut trees that grow wild in the United States are hickory, pecan, black walnut, butternut, beech, chestnut, and hazel.