Draft beer is any beer that is served from large casks or kegs, though the precise meaning of the term varies depending on geography and the intentions of the user. While this has made a single, universal definition of this beverage all but impossible to establish, there are certain typically agreed upon concepts intended or implied when serving or ordering the beer. In the United States and much of the Western world, draft beer has become fairly synonymous with keg beer and is typically served in bars or restaurants from a keg.
The origin of the term draft beer comes from the Old English term “dragen,” which meant "to carry." This was the source of a number of different terms used in the pouring and serving of beer including “draw,” “drag,” and “draught,” which is still used in the United Kingdom. The term draught, or draft, came to be used not only for the process of serving the beer, but for the type of beer itself, drawn from a keg or cask and served to the customers.
Draft beer still typically means beer that is taken from a cask or keg, and though it is used in general for either specific type, there are vast differences between keg beer and cask ale. Keg beer comes from a keg that is pressurized and the beer has typically been pasteurized or filtered, which increases the shelf life of the beer but may reduce the flavor of the beer. Cask ale is a term typically used for beer that is manufactured without pasteurization, so the yeast is still alive and active in the beer. This is usually served traditionally from a cask that must be kept at certain temperatures to ensure safety, and proponents of cask ale insist the flavor is richer and truer to how beer should taste.
Recently, however, beer manufacturers have used the term “draft” for advertising purposes, without recognition of the intended use of the term to refer to a beer served from a cask or keg. Commercial beers sold in bottles or cans have used the word “draft” simply as packaging on a label, in order to appeal to the sense of freshness associated with draft beer.