Before it was a beer style, it was a party.
The first Oktoberfest celebration was held on October 12, 1810, but far from the drinking festival it's become today, this first party was actually held to celebrate a wedding. Ludwig, Crown Prince of Bavaria (who'd later become King Ludwig I) exchanged vows with Princess Therese of Saxe-Hildburghausen, and everyone in Munich was invited to attend. There was music; there was dancing; there were horse races; there was beer. Everyone had such a good time that the royal family decided to host the races again the next year, and the next, and the next. This tradition gave rise to the modern Oktoberfest.
Today, it's the world's largest beer festival. Held annually in Munich, Oktoberfest actually begins in late September, running 16 days and ending the first weekend in October. Some of the traditions of the first Oktoberfest remain -- example, the grounds upon which the festival is held each year are still known as the Theresienwiese, or "Theresa's meadow." But the 6.3 million people who visited in 2014 didn't go to frolick in the grass; they went to drink. You could determine this by the number of arrests made at the festival (720) or the number of people treated by the Bavarian Red Cross for alcohol poisoning (600) or minor alcohol-related scrapes and bumps (7,900). But it's best to just look at the beer: brewers sold 6.5 million liters of beer at this year's Oktoberfest, which equates to about 1,7171,118 gallons or 18,315,925 12-ounce cans.