Caraway seeds are a spice made from the dried fruit of a plant known as Carum carvi. A member of the parsley family, caraway seeds are not technically seeds, but fruits. Nevertheless, they're commonly referred to as caraway seeds in the culinary arts.
Caraway seeds are similar in flavor to aniseed, and in fact you could substitute anise seeds for caraway seeds if you didn't have any.
Caraway seeds are frequently used in baking. The seeds found in most types of rye bread are caraway seeds. Caraway seed is also used in flavoring curries, sausages and even liqueurs. They're sometimes used in pickling and brining as well. It pairs rather well with garlic, and also with pork and cabbage.