Acorn in the context of "Quercus ilex"

A nut is a fruit consisting of a hard or tough nutshell protecting a kernel which is usually edible. In general usage and in a culinary sense, many dry seeds are called nuts, but in a botanical context, "nut" implies that the shell does not open to release the seed (indehiscent).

Most seeds come from fruits that naturally free themselves from the shell, but this is not the case in nuts such as hazelnuts, chestnuts, and acorns, which have hard shell walls and originate from a compound ovary.

An oak is a hardwood tree or shrub in the genus Quercus of the beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne within a cup. The genus is widely distributed in the Northern Hemisphere, with some 500 species, both deciduous and evergreen. Fossil oaks date back to the Middle Eocene. Molecular phylogeny shows that the genus is divided into Old World and New World clades, but many oak species hybridise freely, making the genus's history difficult to resolve.

Ecologically, oaks are keystone species in habitats from Mediterranean semi-desert to subtropical rainforest. They live in association with many kinds of fungi including truffles. Oaks support more than 950 species of caterpillar, many kinds of gall wasp which form distinctive galls (roundish woody lumps such as the oak apple), and a large number of pests and diseases. Oak leaves and acorns contain enough tannin to be toxic to cattle, but pigs are able to digest them safely. Oak timber is strong and hard, and has found many uses in construction and furniture-making. The bark was traditionally used for tanning leather. Wine barrels are made of oak; these are used for aging alcoholic beverages such as sherry and whisky, giving them a range of flavours, colours, and aromas. The spongy bark of the cork oak is used to make traditional wine bottle corks. Almost a third of oak species are threatened with extinction due to climate change, invasive pests, and habitat loss.

A culinary nut is a dry, edible fruit or seed that usually, but not always, has a high fat content. Nuts are used in a wide variety of edible roles, including in baking, as snacks (either roasted or raw), and as flavoring. In addition to botanical nuts, fruits and seeds that have a similar appearance and culinary role are considered to be culinary nuts. Culinary nuts are divided into fruits or seeds in one of four categories:

• True, or botanical nuts: dry, hard-shelled, uncompartmented fruit that do not split on maturity to release seeds; (e.g. hazelnuts)
• Drupes: seed contained within a pit (stone or pyrena) that itself is surrounded by a fleshy fruit (e.g. almonds, walnuts);
• Gymnosperm seeds: naked seeds, with no enclosure (e.g. pine nuts);
• Angiosperm: seeds surrounded by an enclosure, such as a pod or a fruit (e.g. peanuts).

Nuts have a rich history as food. For many indigenous peoples of the Americas, a wide variety of nuts, including acorns, American beech, and others, served as a major source of starch and fat over thousands of years. Similarly, a wide variety of nuts have served as food for Indigenous Australians for many centuries. Other culinary nuts, though known from ancient times, have seen dramatic increases in use in modern times. The most striking such example is the peanut. Its usage was popularized by the work of George Washington Carver, who discovered and popularized many applications of the peanut after employing peanut plants for soil amelioration in fields used to grow cotton.

Westphalian ham (German: Westfälischer Schinken) is a ham that was originally produced from acorn-fed pigs raised in the forests of Westphalia, Germany. The resulting meat is dry cured and then smoked over a mixture of beechwood and juniper branches.

The hams are prepared for consumption solely by the process of smoking, which preserves them, and are typically eaten thinly sliced in their preserved state without additional cooking.

Coffee substitutes are non-coffee products, usually without caffeine, that are used to imitate coffee. Coffee substitutes can be used for medical, economic and religious reasons, or simply because coffee is not readily available. Roasted grain beverages are common substitutes for coffee.

In World War II, acorns were used to make coffee, as well as roasted chicory and grain. Postum, a bran and molasses beverage, also became a popular coffee substitute during this time. During the American Civil War coffee was also scarce in the Southern United States:

A nut is a fruit consisting of a hard or tough nutshell protecting a kernel which is usually edible. In general usage and in a culinary sense, many dry seeds are called nuts. In a botanical context, "nut" implies that the shell does not open to release the seed (indehiscent).

Most seeds come from fruits that naturally free themselves from the shell, but this is not the case in nuts such as hazelnuts, chestnuts, and acorns, which have hard shell walls and originate from a compound ovary. The general and original usage of the term is less restrictive, and many nuts (in the culinary sense), such as almonds, pistachios, and Brazil nuts, are not nuts in a botanical sense. Common usage of the term often refers to any hard-walled, edible kernel as a nut. Nuts are an energy-dense and nutrient-rich food source.