The fifth of May which is observed in Mexico and Mexican-American communities in the United States to commemorate the Mexican victory over the French in the Battle of Puebla in 1862 WordNet 3.0 & Open English WordNet

Cinco de Mayo is a yearly celebration held on May 5 to celebrate Mexico's victory over the Second French Empire at the Battle of Puebla in 1862, led by General Ignacio Zaragoza. Wikipedia

Annual celebration held on May 5 Wikidata

A national celebration in Mexico, commemorating the victory of Mexican forces led by General Ignacio Zaragoza over the French expeditionary forces in the Battle of Puebla on May 5, 1862, also celebrated widely by immigrants living in the United States. Wiktionary