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, a wide variety of 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. 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,1 are not nuts in a botanical sense. Common usage of the term often refers to any
hard-walled, edible kernel as a nut.2 Nuts are an energy-dense and nutrient-rich food source.3