Beer, generally, is an alcoholic beverage produced through the fermentation of sugars suspended in an aqueous medium, and which is not distilled after fermentation. The unfermented sugar solution, called wort, is obtained from steeping, or "mashing," malted grains, usually barley. Alcoholic beverages made from the fermentation of sugars derived from non-grain sources — fruit juices or honey, for example — are generally not called "beer," despite being produced by the same yeast-based biochemical reaction.

The process of beer production is called brewing. Because the ingredients used to make beer differ from place to place, beer characteristics such as taste and color vary widely, and consequently its style or classification.

Brewing dates back to at least the 5th millennium BC and is recorded in the written history of Ancient Egypt and Mesopotamia.

Beer is considered to be a social lubricant in many societies. Various social traditions and activities are associated with beer drinking, such as buying a round, pub crawling, or various pub games.