Adjunct lagers, arguably the world's most popular beer style based on production volume, is a variation of the pale lager or pilsner styles where corn, rice, or other non-barley grains are added to the mash bill. This style was popularized after Prohibition and generally thought to have been the result of cost saving and rationing measures by lager breweries during World War 2. After the war, tastes apparently changed and the style persisted; it's sometimes referred to as 'macro' lager.
Adjunct lagers are generally light-bodied with a light hop impression and a clean, crisp malt character. Quality, from a flavor point of view, is very variable within this style and many cheaper examples use a higher proportion of non-malt additives. Alcohol content is typically between 3.5-5% ABV, with the upper end of the range being preferable if one is to get a true lager mouthfeel.
There are numerous examples from all countries around the world including: Budweiser, Miller High Life, Modelo, Tsingtao, Quilmes, and even some craft examples using the monikers of 'Classic American' and 'Mexican Lager' like Capitol Brewery's Capitol 1900.