A hazelnut is closely related to the cob nut and filbert nut and they are often mistaken. A cob is roughly spherical to oval, about 15–25 mm (½-1”) long and 10–15 mm in diameter, with an outer fibrous husk surrounding a smooth shell. A filbert is more elongated, being about twice as long as it is round. The nut drops away from the shell when it ripens so that they rattle if you shake them, about 7–8 months after pollination. The kernel of the seed is edible and used raw or roasted, or ground into a paste. The seed has a thin, dark brown skin which is sometimes removed before cooking.
