Although lager is a style of beer, saying 'lager' will produce a Yuengling Lager beer.
Interestingly, Pilsener is now a term applied to beer that doesn't meet strict Northern European purity standards and cannot be called lager.
Also used with a modifier (-lout) to describe the behaviour of young (usually) men after cosuming large amounts of this very drinkable beer. This usage may now be archaic, being largely an invention of the British tabloid press in the 1980's.
"LAGER LOUTS TERRORISE TOWN CENTRE"
Pilsner is a style from Pilzn, which is a Czech style lager. It is what today's standard lagers are meant to be, but often miss the points of the style.
The term 'lager' is German for aging, which refers to the 'secondary fermentation' where little CO2 is produced, yet yeast is still inside the vessel. Ales undergo little or no secondary fermentation, and get sent through a centrifuge or diatomaceous earth filter on the way to the bright tank for packaging. Some ales get racked directly to a cask for cask ales.