Cinco de mayo (May 5) is the celebration of the Mexican Army's defeat of the French during the Battle of Puebla on May 5, 1862. Cinco de mayo does NOT celebrate Mexican Independence Day (That date is September 16.), and it is actually more regionally celebrated in Mexico (mostly in the state of Puebla). As a celebration of Mexican heritage, it is very popular in the United States.
Feliz dia, amigos!