Key difference: All beer falls under two primary categories: ales and lager. Lagers are a type of bottom fermenting beer. Pilsner is a type of lager that originated in Plzeň (Pilsen), a town located in Bohemia.

There are many different types of beers out there, each one is categorized and labeled according to the way it is fermented and processed. They are also divided and classified based on its taste, which varies depending on the ingredients used. However, all beer falls under two primary categories: ales and lager. All other beers such as pilsner, stouts, porters, etc. are categorized as styles under these two main categories.

The primary difference between ales and lager is the way they are fermented. Ales are fermented using top-fermenting yeasts. The yeast is named as such due to the fact that it tends to collect at the surface of the beer as it is fermenting. Alternately, the lager is fermented using a bottom fermenting yeast, i.e. a type of yeast that does not rise to the surface. Another difference between the two is the temperature they are fermented at. Lagers are fermented at cold temperatures throughout the entire process; whereas ales are fermented at warmer temperatures. Once the ale is fermented, it is refrigerated which stops the fermentation process. Lager, on the other hand, continues to ferment after refrigeration.

Following their definitions, it can be noted that lager is a type of beer. Pilsner, on the other hand, is a specific style of beer; one that is officially categorized as a lager. A pilsner is a type of lager; specifically it is a type of pale lager. The most identifying feature of a pale lager and a pilsner is its color. It has a very pale to golden-color; the typically color that most people associate with beer.