Acorns are the edible nuts of oak trees (genus Quercus), an important food source for many cultures, particularly indigenous peoples in North America, Europe, and Asia. They're a good source of protein, carbohydrates, fat, and fiber.
Acorn flavor ranges from sweet and nutty to bitter and astringent depending on the oak species and how the nuts are prepared; species like white oak and Emory oak produce more palatable, lower-tannin acorns than others. Because raw acorns are high in bitter tannins, they're traditionally leached in water before being ground into flour or boiled, roasted, or made into porridge; acorn flour has been used for breads, cakes, and other baked goods, and in some regions acorns were fermented into alcoholic beverages.
Acorns are still eaten today in parts of Korea, where they're dried, roasted, or made into a jelly (dotorimuk), and in the American Southwest, where Navajo and other tribes continue to use them in traditional cooking.
Beyond food, acorns have been used as animal feed, for dye, in traditional medicine, and their tannins in tanning leather; acorn consumption has declined broadly with the rise of commercially produced food, though there's renewed interest in traditional acorn-based cooking.