A soup is a dish obtaining most of its flavor from a liquid created by extracting flavor from solids such as meat and vegetables.
Soup- or broth-making is a slow, moist-heat method extracting into liquid flavor from solids (typically proteins and vegetables). The resulting flavorful liquid may be served with the solids the flavor was extracted from (possible puréed), fresh solids may be added, or in some cases, there may be no solids at all. In any case, the intent is for the liquid to be the primary flavor component.
This contrasts with stew, where the solids are the primary flavor component. For details on the differences, refer to the question, Difference between soup and stew.
