Welcome to the Cinco de Mayo (Spanish for "Fifth of May") holiday!
Many Americans think this is the Mexican Independence Day. It's not. It's not even a national holiday in Mexico. It's celebrated in the U.S. more than in Mexico. Mexico declared its independence from mother Spain on midnight, September 15, 1810. (And it took 11 years before the first Spanish soldiers were told and forced to leave Mexico.)
May 5th is a regional holiday in Mexico, primarily celebrated in the state of Puebla, with some limited recognition in other parts of Mexico. The holiday commemorates the Mexican army's unlikely defeat of French forces at the Battle of Puebla on May 5, 1862.
While Cinco de Mayo has limited or no significance nationwide in Mexico, the date is observed in the United States and other locations around the world as a celebration of Mexican heritage and pride.