Some call them hazelnuts, some call them filberts. In fact, some people call them cobnuts, at least in England.
The terminology is really a mess. In this country a filbert usually means an imported hazelnut, because we have a couple of native hazelnuts of our own, and there's no such thing as a cob. In England, though, any hazelnut is a hazelnut but filberts and cobs are two specific varieties, a filbert being elongated, rather than round, and completely covered by its husk. (Just to make trouble, the most famous cob, the Kentish cob, is technically a filbert.)
The ancient Greeks called hazelnuts pontika because they associated them with the kingdom of Pontus on the Black Sea. The Arabs picked up the name as bunduqa and used plenty of hazelnuts in medieval stews and sweets.
And then a funny thing happened in medieval Moorish Spain: Bunduqa came to be a word for meatball, though a hazelnut-sized meatball would be remarkably small. The Middle East does occasionally make a cult of tiny meatballs, such as the Turkish yuvarlama, but it's doubtful that the Moorish bunduqas were ever hazelnut-sized . . . particularly since there are medieval recipes that say to make them as big as oranges.
This probably came about because the word bunduqa was also used for the rock or metal ball thrown by a catapult or cannon. So these weren't meat hazelnuts--they were more like meat bombs.
In any case, the word al-bunduqa eventually made it into Spanish, where it became the word for meatball, albondiga. And where an albondigon ("big meatball") is what we'd call a meatloaf. Pally, there's no hazelnut in the world that big.