A nut is a hard-shelled indehiscent fruit of some plants. While a wide variety of dried seeds and fruits are called nuts in English, only a certain number of them are considered by biologists to be true nuts. Nuts are an important source of nutrients for both humans and wildlife.

Nuts are a composite of the seed and the fruit, where the fruit does not open to release the seed. Most seeds come from fruits, and the seeds are free of the fruit, unlike nuts such as hazelnuts, hickories, chestnuts and acorns, which have a stony fruit wall and originate from a compound ovary. Culinary usage of the term is less restrictive, and some nuts as defined in food preparation, like pistachios and Brazil nuts, are not nuts in a biological sense. Everyday common usage of the term often refers to any hard-walled, edible kernel as a nut.

A nut in botany is a simple dry fruit with one seed (rarely two) in which the ovary wall becomes very hard (stony or woody) at maturity, and where the seed remains attached or fused with the ovary wall. Most nuts come from the pistils with inferior ovaries (see flower) and all are indehiscent (not opening at maturity). True nuts are produced, for example, by some plant families of the order Fagales.

Nut, NUT, Nuts or NUTS may refer to:

In botany, a fruit is a part of a flowering plant that derives from specific tissues of the flower, mainly one or more ovaries. Fruits are the means by which many plants disseminate seeds. Many plants bearing edible fruits, in particular, have propagated with the movements of humans and animals in a symbiotic relationship as a means for seed dispersal and nutrition, respectively; in fact, humans and many animals have become dependent on fruits as a source of food. Fruits account for a substantial fraction of the world's agricultural output, and some (such as the apple and the pomegranate) have acquired extensive cultural and symbolic meanings.

The section of a fungus that produces spores is also called a fruiting body.

In common language usage, fruit normally means the fleshy seed-associated structures of a plant that are sweet and edible in the raw state, such as apples, oranges, grapes, strawberries, and bananas. On the other hand, the botanical sense includes many structures that are not commonly called "fruits", such as bean pods, corn kernels, wheat grains, and tomatoes.