Canned tomato condensed soup

Canned soup can be condensed, in which case it is prepared by adding water (or sometimes milk), or it can be "ready-to-eat," meaning that no additional liquid is needed before eating. Canned soup (condensed with liquid added, or "ready-to-eat") can be prepared by heating in a pan, on the stovetop or in the microwave. Such soups can be used as a base for homemade soups, with the consumer adding anything from a few vegetables to eggs, vegetables, cream or pasta.

Condensing soup allows soup to be packaged into a smaller can and sold at a lower price than other canned soups. The soup is usually doubled in volume by adding a "can full" of water or milk (about 10 ounces).

Since the 1990s, the canned soup market has burgeoned with soups marketed as "ready-to-eat," which require no additional liquid to prepare. Microwaveable bowls have expanded the ready-to-eat canned soup market even more, offering convenience (especially in workplaces) and are popular lunch items.
Source: http://en.wikipedia.org/wiki/Soup#Canned_soup