Irish boiling bacon is a cut of pork that is very different from American-style bacon. American-style bacon comes from the belly of the pig, while Irish boiling bacon comes from the back or shoulder.
Because Irish boiling bacon is derived from the pork shoulder or back, it is much leaner than American-style bacon. In flavor, it resembles ham. Boiling bacon is usually cured but not necessarily smoked, and may be sold in large chunks rather than in strips like American-style bacon.
Irish boiling bacon is most famously used in the traditional Irish dish "Bacon and Cabbage." It is also used in many casserole, bean and pasta dishes.
Corned Beef and Cabbage, which many Americans consider to be classic Irish fare, is actually a variation on Bacon and Cabbage, which was created by Irish-American immigrants when they discovered how cheap beef was in the New World. Bacon and Cabbage is by far the more "authentic" dish.
Historically, pork was the favored protein of most Irish people, as beef was considered too valuable for everyday eating.
In Ireland, all cuts of pork, besides the leg, are called bacon. This applies whether these cuts are cured or uncured, smoked, or fresh. This can lead to confusion when attempting to purchase "Irish bacon."