Bacon is cured and/or smoked pork belly. Other cuts of pork are treated in the same manner but given different names. For example gammon comes from the leg and kassler is a loin chop. Pancetta and prosciutto, and their numerous cousins are a dry salted, unsmoked and air dried bacon.
Bacon is either wet or dry cured. In wet curing the pork is immersed in a brine solution for several days. The brine usually includes saltpetre (a preservative) sugar and spices. In dry cured bacon the pork is rubbed with coarse salt and buried in the salt for some days. After curing the bacon is ether air dried (e.g. pancetta) or smoked. The smoking is done at a temperature that cooks the meat unless it is cold smoked or green bacon.
Modern bacon is cured in brine and also 'pumped' (injected with brine to speed up the curing process). Much technical expertise is used to increase the water content of the final product at the expense of its flavour but not the manufacturer's profit margin.