Budweiser is the name for two separate popular brands of beer, one brewed in the Czech Republic and one based in the United States.
The original use of the term Budweiser was used to refer to beer from the city of České Budějovice in Bohemia (the modern Czech Republic) since 1265. Derived from the German name for the town, Budweis, something from Budweis being Budweiser.
The largest (but not the only) brewery in Ceske Budejovice has long exported beer under the "Budweiser" brandname, and in many European countries this is the only beer that may be sold as "Budweiser". In some places where it competes with the American Budweiser it is marketed by the brewer Budejovicky Budvar using the names "Budvar", "Budweiser Budvar", and "Budejovicky Budvar". It recently started having limited distribution in the USA under the name "Czechvar".
The United States Budweiser is the best-selling brand of beer sold by Anheuser-Busch, the world's second largest brewing company, based in Saint Louis, Missouri. As the name implies, it was originally brewed in imitation of the famous Czech beer, but over the decades has developed its own style which has proved very commercially successful. It is brewed in the lager style using mass production techniques. It is very lightly flavoured, and heavily carbonated, and probably the mildest-tasting beer of any of the internationally-popular lagers. Despite its wide commercial success in the United States, it has a very poor reputation with foreign beer drinkers, and domestically is seen as the antithesis of the more characterful beers produced by microbrews.
Budweiser beer deteriorates quickly with age or excessive heat, so to ensure quality the company has fairly stringent requirements for handling and sale. There are numerous Budweiser breweries located around the nation, many of which offer tours with free samples. One thing tour guides will often do is when their group reaches the hospitality room is to ask a few volunteers to try what they refer to "punished Budweiser." This is beer stored in a room for two weeks in a high temperature enviornment. First they will have the volunteers try fresh Budweiser, and then try the "punished" beer. Visitors often find this beer is not as good as fresh beer.
Anheuser-Busch has a market share in the United States of about 50% for all of its brands of beer combined. The company is known for its sports sponsorships, video game sponsorship (Tapper), and (often) humorous advertisements. Advertising campaigns have included a nude Ganymede grasping a beer bottle and borne aloft by a bald eagle, frogs saying 'bud-wei-ser', lizards doing the same, and Clydesdale horses. Recently, Miller Brewing had begun a series of commercials in which "referees" were calling "penalties" on people drinking Bud Light, and the "referees" replaced the beer with Miller beer. Anheuser-Busch responded by making their own series of "referee" commercials that shows "referees" taking Bud Light for themselves. Anheuser-Busch is also known for its repeated legal attempts to obtain complete control of the Budweiser trademark, which have been generally unsuccessful.
In the United States and most of Latin America, the American beer is the only one which may be sold under the name "Budweiser". In some countries where the Czech brew has rights to that name, the American beer is sold as "Bud", in some European countries as "Anheuser Busch", since the Czech beer is sold as "Budweiser".