There are three categories when classifying beer. They are ales, lagers and the remaining beers come under specialty beers.

The main difference between a lager and ale is the type of yeast used in fermentation.

Ales
Ales are usually higher in alcohol and will be noticeable fuller and more complex.

Lagers
Lagers tend to be lighter in color and usually taste drier than ales. They are generally less alcoholic and complex.

Specialty Beers
Specialty beers are either ales, lagers, or a hybrid of the two that will contain other ingredients that cause it to not fit into a true ale or lager style.