Base malts make up the majority of the grist in all-grain beer. This group includes pale malt, Pilsner malt, Vienna malt, Munich malt, Mild ale malt, and more; there are also non-barley base malts like wheat malt and rye malt.
Base malts can be named based on the formation of corns on the barley stalk (2-row vs. 6-row), the barley variety (e.g., Maris Otter, Golden Promise, etc), or the region in which the barley was grown or malted (America, England, Moravia, etc).
American base malt is generally mild and fairly neutral; British malts tend to be maltier, bready, and biscuit-like. The European climate gives malts made from Continental barley a clean, “elegant” character. Pilsner malt has a soft, delicate maltiness that practically defines pale lagers. “High-kilned” (heated to a higher temperature at the end of the malting process) base malts are responsible for the dark, malty lagers of Europe and have found a home in many ales because of their unique character. Munich and Vienna malts are the prime examples of high-kilned malts, although mild ale malt belongs to this category too. The darker color lends these malts a more toasty, malty flavor than you get from lighter base malts.