Wiki article on this topic:
Soup is a primarily liquid food, generally served warm or hot , that is made by combining ingredients of meat or vegetables with stock, or water. Hot soups are additionally characterized by boiling solid ingredients in liquids in a pot until the flavors are extracted, forming a broth.
In traditional French cuisine, soups are classified into two main groups: clear soups and thick soups. The established French classifications of clear soups are bouillon and consommé. Thick soups are classified depending upon the type of thickening agent used: purées are vegetable soups thickened with starch; bisques are made from puréed shellfish or vegetables thickened with cream; cream soups may be thickened with béchamel sauce; and veloutés are thickened with eggs, butter, and cream. Other ingredients commonly used to thicken soups and broths include egg, rice, lentils, flour, and grains; many popular soups also include pumpkin, carrots, and potatoes.
Soups are similar to stews, and in some cases there may not be a clear distinction between the two; however, soups generally have more liquid than stews.
Evidence of the existence of soup can be found as far back as about 20,000 BC. Boiling was not a common cooking technique until the invention of waterproof containers. Animal hides and watertight baskets of bark or reeds were used before this. To boil the water hot rocks were used. This method was also used to cook acorns and other plants.
The word soup comes from French soupe , which comes through Vulgar Latin suppa from a Germanic source, from which also comes the word "sop", a piece of bread used to soak up soup or a thick stew.
The word restaurant was first used in France in the 16th century, to refer to a highly concentrated, inexpensive soup, sold by street vendors, that was advertised as an antidote to physical exhaustion. In 1765, a Parisian entrepreneur opened a shop specializing in such soups. This prompted the use of the modern word restaurant for the eating establishments.