Cloves are a spice made from the flower buds of an evergreen tree called, appropriately enough, the clove tree. Clove flower buds are harvested in their immature state, and then dried.
Cloves can be used whole or ground, and they have a very strong, pungent flavor and aroma. Whole cloves are shaped like a small, reddish brown spike, usually around one centimeter in length, with a bulbous top.
Cloves are used to flavor sauces, soups and rice dishes, notably a number of traditional Indian dishes, and it's one of the components of garam masala.
Whole cloves are either removed before serving or picked out of the dish. Even when cooked, whole cloves have a very hard, woody texture and not only would their flavor would be overpowering, someone could break a tooth biting into one.
A prudent cook will exercise care to make sure that none end up in the finished dish. Conversely, a prudent diner will exercise care when when tucking into biryani dishes, as it's not unheard of to find whole cloves, whole peppercorns and even whole caradamom pods lurking therein. And yet, one doesn't complain, as this practice seems to correlate very strongly with excellent biryani.
Cloves also feature in any number of desserts, especially ground cloves, and particularly around the holidays. Think eggnog or pumpkin pie spice. One of my favorite uses for cloves is for making mulled wine. Cloves are also one of the the key spices used in making the classic béchamel sauce.
Cloves are often paired with cinnamon or nutmeg, but in general, it's a good idea to use cloves sparingly.
Which is just as well, since they can be expensive. Not that you can't get them cheaply, but it won't do to simply grab any jar of cloves you see in the spice aisle. For one thing, supermarkets will charge whatever they can get away with.
Also, some of the fancy spice companies sell what they call "gourmet cloves." Also known as Penang cloves, these high-end cloves are individually selected by hand to ensure that each one is flawlessly shaped.
Thus the unwitting consumer can needlessly spend $8–9 on a jar of whole cloves, when a plastic package of them can be had a few aisles over in the Hispanic food section for less than $2. The label might say clavos de olor, or simply clavos.
Cloves are grown in India and Madagascar, but if there's a country on earth that is most closely associated with the production of cloves, it is certainly Indonesia. (Think clove cigarettes.)
Indeed, so lucrative was the clove trade originating in an island chain once known as the Spice Islands (now part of Indonesia), that in 1667, following the Second Anglo-Dutch War, the British ceded the islands to the Dutch in exchange for a faraway settlement then known as New Amsterdam. Thus did the Dutch swap Manhattan for cloves. Remember that next time someone lights up a Kretek on the stoop outside your brownstone.