Lager is beer which has been brewed and conditioned at low temperature. lagers can be pale, amber, or dark. pale lager is the most widely consumed and commercially available style of beer. the term "lager" comes from the german for "storage", as the beer was stored before drinking – traditionally in the same cool caves it was fermented in. as well as maturation in cold storage, most lagers are distinguished by the use of saccharomyces pastorianus, a "bottom-fermenting" yeast that ferments at relatively cold temperatures.

Source: Wikipedia