Soup is a primarily liquid food, generally served warm or hot (but may be cool or cold), 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. 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 (broth) 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 (which probably came in the form of clay vessels). 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 restaurant (meaning "[something] restoring") 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.
In the US, the first colonial cookbook was published by William Parks in Williamsburg, Virginia, in 1742, based on Eliza Smith's The Compleat Housewife; or Accomplished Gentlewoman's Companion, and it included several recipes for soups and bisques. A 1772 cookbook, The Frugal Housewife, contained an entire chapter on the topic. English cooking dominated early colonial cooking; but as new immigrants arrived from other countries, other national soups gained popularity. In particular, German immigrants living in Pennsylvania were famous for their potato soups. In 1794, Jean Baptiste Gilbert Payplat dis Julien, a refugee from the French Revolution, opened an eating establishment in Boston called "The Restorator", and became known as the "Prince of Soups". The first American cooking pamphlet dedicated to soup recipes was written in 1882 by Emma Ewing: Soups and Soup Making.
Since the 1990s, the canned soup market has burgeoned, with non-condensed soups marketed as "ready-to-eat", so they 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 making for popular lunch items. In response to concerns over the negative health effects of excessive salt intake, some soup manufacturers have introduced reduced-salt versions of popular soups.
Cold soups are a particular variation on the traditional soup, wherein the temperature when served is kept at or below room temperature. They may be sweet or savory. In summer, sweet cold soups can form part of a dessert tray. An example of a savory chilled soup is gazpacho, a chilled vegetable-based soup originating from Spain. Vichyssoise is a cold puree of potatoes, leeks, and cream.