The easy answer to "what is Cinco de Mayo" is it's the Spanish words for May 5th. It's not Mexico's Independence Day - that's later in the year on September 16.
Cinco de Mayo is celebrated in MexicoÂ because the Mexicans fought the FrenchÂ at PueblaÂ on May 5, 1862 and pulled off a very unlikely victory.Â In the US, it's a holiday of Mexican pride.Â Or that's what it's supposed to be. For some folks, it just seems like an excuse to get drunk.Â I'm not quite sure how the holiday is treated in Mexico, I imagine something like Memorial Day in the US.
At any rate, happy 5th of May to you no matter what you are doing