Bacon is a cured meat prepared from a pig. It is first cured using large quantities of salt, either in a brine or in a dry packing; the result is fresh bacon (also green bacon). Fresh bacon may then be further dried for weeks or months (usually in cold air), boiled, or smoked. Fresh and dried bacon must be cooked before eating. Boiled bacon is ready to eat, as is some smoked bacon, but either may be cooked further before eating.
Bacon is prepared from several different cuts of meat. It is usually made from side and back cuts of pork, except in the United States, where it is almost always prepared from pork belly (typically referred to as "streaky", "fatty", or "American style" outside of the US). The side cut has more meat and less fat than the belly. Bacon may be prepared from either of two distinct back cuts: fatback, which is almost pure fat, and pork loin, which is very lean. Bacon-cured pork loin is known as back bacon.
Bacon may be eaten smoked, boiled, fried, baked, or grilled, or used as a minor ingredient to flavor dishes. Bacon is also used for barding and larding roasts, especially game birds. The word is derived from the Old High German bacho, meaning "buttock", "ham" or "side of bacon", and cognate with the Old French bacon.
In continental Europe, this part of the pig is usually not smoked like bacon is in the United States; it is used primarily in cubes (lardons) as a cooking ingredient, valued both as a source of fat and for its flavor. In Italy, this is called pancetta and is usually cooked in small cubes or served uncooked and thinly sliced as part of an antipasto.
Meat from other animals, such as beef, lamb, chicken, goat, or turkey, may also be cut, cured, or otherwise prepared to resemble bacon, and may even be referred to as "bacon". Such use is common in areas with significant Jewish and Muslim populations. The USDA defines bacon as "the cured belly of a swine carcass"; other cuts and characteristics must be separately qualified (e.g., "smoked pork loin bacon"). For safety, bacon must be treated for trichinella, a parasitic roundworm which can be destroyed by heating, freezing, drying, or smoking.
Bacon is distinguished from salt pork and ham by differences in the brine (or dry packing). Bacon brine has added ingredients, most notably sodium nitrite, and occasionally sodium nitrate or saltpeter, added to cure the meat; sodium ascorbate or erythorbate are added to accelerate curing and stabilize color. Flavorings such as brown sugar or maple are used for some products. If used, sodium polyphosphates are added to improve sliceability and reduce spattering when the bacon is pan fried. Today, a brine for ham, but not bacon, includes a large amount of sugar. Historically, "ham" and "bacon" referred to different cuts of meat that were brined or packed identically, often together in the same barrel.