The hazelnut is the fruit of the hazel tree and therefore includes any of the nuts deriving from species of the genus Corylus, especially the nuts of the species Corylus avellana. They are also known as cobnuts or filberts according to species.

Hazelnuts are used as a snack food, in baking and desserts, and in breakfast cereals such as muesli. In confectionery, they are used to make praline, and also used in combination with chocolate for chocolate truffles and products such as chocolate bars and hazelnut cocoa spreads such as Nutella. They are also used in Frangelico liqueur. Hazelnut oil, pressed from hazelnuts, is strongly flavored and high in monounsaturated fat. It is used as a cooking oil and as a salad or vegetable dressing.

Hazelnut tree, 

A hazelnut cob is roughly spherical to oval, about 15–25 millimetres (5⁄8–1 inch) long and 10–15 mm (3⁄8–5⁄8 in) in diameter, with an outer fibrous husk surrounding a smooth shell, while a filbert is more elongated, being about twice as long as its diameter. The nut falls out of the husk when ripe, about seven to eight months after pollination. The seed is edible and consumed raw, roasted or ground into a paste. The seed has a thin, dark brown skin, which is sometimes removed before cooking.