The fruit of the hazel tree, hazelnuts are globe-shaped with a hard brown shell. They were eaten by the ancient Greeks and Romans, both for their nutritional and medicinal qualities. Hazelnuts are also known as "filberts," since the nuts' peak harvesting time coincided with the feast of St. Filbert (August 20). 

Botanically, the hazelnut is an achene, a dry fruit containing a single seed, that may be round or oblong, measuring up to 3 cm in length and 2 cm across. The fruits grow in pairs or groups of three. 

Its green lobed husk covers all or part of the fruit. The yellowish seed is contained in a shell and cover with a thin skin.