Lager styles are a relatively recent on the global beer scene, when one considers the centuries of ale brewing that predated the production of lagers. The simple difference between a lager and an ale is that the yeast employed for fermentation of a lager works at a cooler temperature and sinks to the bottom of the fermentation vessel, while ale yeasts work at higher temperatures and rise to the top of the vessel. Hence lagers are "bottom fermented"
The US brewing industry had a hand in the rise of pale lager in the early 20th Century. The American climate necessitated the advent of refrigeration for the distribution of food over long distances during scorching summer months. Such advances also permitted the establishment of breweries in climates where God never intended, a fact probably not lost on some God-fearing citizens who took matters into their own hands during the years between 1919 and 1933.
Amber Lagers. Amber lagers are a vaguely defined style of lager much favored by US lager brewers. They are darker in color, anywhere from amber to copper hued, and generally more fully flavored than a standard pale lager. Caramel malt flavors are typical and hopping levels vary considerably from one brewery to the next, though they are frequently hoppier than the true vienna lager styles on which they are loosely based. Alcohol levels are generally a maximum of 5% ABV.
Black/Schwarz Beer. Originally brewed in Thuringia, a state in eastern Germany, these lager style brews were known to be darker in color than their Munich counterparts. Often relatively full-bodied, rarely under 5%ABV, these beers classically feature a bitter chocolate, roasted malt note and a rounded character. Hop accents are generally low. This obscure style was picked up by Japanese brewers and is made in small quantities by all of Japan's major brewers. Schwarz beers are not often attempted by US craft brewers.
Bock. Bocks are a specific type of strong lager historically associated with Germany and specifically the town of Einbeck. These beers range in color from pale to deep amber tones, and feature a decided sweetness on the palate. Bock styles are an exposition of malty sweetness that is classically associated with the character and flavor of Bavarian malt. Alcohol levels are quite potent, typically 5-6% ABV. Hop aromas are generally low though hop bitterness can serve as a balancing factor against the malt sweetness. Many of these beers' names or labels feature some reference to a goat. This is a play on words in that the word bock also refers to a male goat in the German language. Many brewers choose to craft these beers for consumption in the spring (often called Maibock) or winter, when their warmth can be fully appreciated.
Dark Lager/Dunkel. Dunkel is the original style of lager, serving as the forerunner to the pale lagers of today. They originated in and around Bavaria, and are widely brewed both there and around the world. This is often what the average consumer is referring to when they think of dark beer. At their best these beers combine the dryish chocolate or licorice notes associated with the use of dark roasted malts and the roundness and crisp character of a lager. Examples brewed in and around Munich tend to be a little fuller-bodied and sometimes have a hint of bready sweetness to the palate, a characteristic of the typical Bavarian malts used.