ring-shaped cake, or doughnut
From the Latin suavillum, a ciambella was originally a ring-shaped yeast bread, double baked til hard and lasting, taken by shepherds into the mountains. These days it's usually a rich ring cake, called either ciambella or ciambellone.
A ciambella (or more often, ciambellina) is also a doughnut. Several regions have their own specialities:
ciambella all'acqua, 'water donut', is first boiled in water and then baked
ciambella a cancello, or ciambelle ruzze from Lazio, are made with aniseed and wine. The Castelli Romani are also famous for the ciambelle al vino, made with wine (that all evaporates during the cooking, so it's okay to let the kids have some, too).
ciambella ellenese, a small, knot-shaped donut, is made with cinnamon and covered with rose water.
ciambella ferrarese, of Ferrara, is a baked donut made with flour, sugar, eggs and butter.
ciambella frastagliata: from the Marche, made with lots of eggs and mistrà, then boiled, dried, sliced in half and baked until crisp. The name means 'jagged doughnut.'
The Calabrian version is called cuddrurieddru.