Husk (or hull) in botany is the outer shell or coating of a seed. In the United States, the term husk often refers to the leafy outer covering of an ear of maize (corn) as it grows on the plant. Literally, a husk or hull includes the protective outer covering of a seed, fruit, or vegetable.

It can also refer to the exuvia of insects or other small animals left behind after moulting.

The term husk dates to c.14, it is probably based on Middle Dutch word huusken meaning 'little house', which is derived from hūs meaning house.

In cooking, hull can also refer to other waste parts of fruits and vegetables, notably the cap or sepal of a strawberry.

Grains such as wheat and barley have husks. The grains are the entire seed of a plant. The seed of a grain (which the grain industry calls a "kernel") is made up of three key edible parts – the bran, the germ, and the endosperm – which are all protected by an inedible husk that protects the kernel from damage by sunlight, pests, water and disease.

In Hazel trees, the nut is surrounded by a short leafy husk (which is technically an involucre). This leaf-like husk encloses most of the nut. It starts off green and will fade to brown at the end of the season. Usually, the ripe nut falls out of (or can be separated from) the husk some 7–8 months after pollination has occurred.

In some places, both shells and the husks of walnuts (Juglans regia L.) which are produced as waste crops during the fruit harvesting and processing, are sometimes burned as fuel for heating purposes. In 2019, it has been demonstrated that the walnut green husk could be valued as a source of different natural bio-active compounds with excellent antioxidant and antimicrobial properties. As well as cosmetic uses. An organic compound Naphthalenone, (derivative of Naphthalene) is found in green walnut husks of Juglans mandshurica Maxim. for various uses. Juglans nigra, black walnut, husks have antioxidant potential. Confusingly, Walnut husks are also called hulls as well. Rhagoletis juglandis, also known as the 'walnut husk fly' is a common pest of walnuts. The larvae are small and live under the surface of the husk of the walnut. They cause damage to the fruit and husks which then become difficult to remove. The husk fly also infests ripe apricot and peach fruits, usually if infested walnuts are located within flying distance.

Some fruit shell and hull derived bio-adsorbents have also been used for wastewater treatment purposes. For example, the almond hull and shell have been used to remove metals such as Pb, Cd, and Co in various quantities. Iranian almond (Prunus amygdalus L.) hulls have antioxidant and anti-radical properties.