1 : literally, the fifth of May

2a : a holiday celebrated by millions of Mexican nationals in America with notable festivity and drunkenness to commemorate their heritage and pride in the greatness of a country they couldn't wait to leave

2b : a holiday celebrated in Mexico by a small number of Mexicans with overwrought sadness and drunkenness to lament their expulsion from America by the Border Patrol <see also, el día de los muertos>
We wildly waved the la Bandera de México at the East LA Cinco de Mayo festival to protest those nasty gringos who won't defund the Border Patrol so they can afford to increase our welfare checks and medical care.

"Happy Cinco de Mayo! Now go kill some Gringo Bastardos!" Jose Angel Gutierrez
by J. Myars May 5, 2009
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A beer-fest that occurs on May 5 of the year, with lots of tequila and margaritas.
Man, I got so wasted on Cinco de Mayo!
by melissa morton May 11, 2003
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This started out as a tragedy in the late eighteenth century. It is a well known fact that mexicans love mayonnaise. A large steam tanker of this condiment was crossing the gulf of mexico from florida when a large storm occured, sinking the tanker. The horrified mexicans witnessed this and named the day of the sinking, May 5, a national holiday of drowning their worries with corona.
"O no-o! Did-o you hear-o about the cinco de mayo??!!"
by G Love July 6, 2006
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Contrary to a surprising public belief, Cindo de Mayo is not a holiday of independance. It celebrates the battle of Puebla(1862), when 2000 Mexican soldiers beat back 6000 French attackers under the rule of Napolean III. This is also the day that Napolean died. So far as I understand it, the holiday is celebrated much more in the US than in Mexico. We can thank the Corona beer company and college students for this.
"Cinco de Mayo is not Mexican Independance Day. That is September 16th."
by plasticus May 7, 2004
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A few of my gringo friends ask me the meaning of Cinco de Mayo every year so I thought I would give the full unabridged and comprehensive answer here.

It all started on a cool April morning in 1843 in Mexico. It was the middle of the Mexican war of independence against their Mayan overlords. General Chimichanga was leading an offensive for the Mexican army and was marching north to meet the Mayans at Fajita Hill. He knew he would be out-numbered so he sent his mariachi band to contact the Burrito Boys in Tijuana to request their assistance in battle. He was not sure if they would agree or even arrive in time for the battle (they were located 23.5 miles away). When General Chimichanga arrived at Fajita Hill on May 5 he was amazed to find the Burrito Boys and their leader Commander Nacho Cheese got there first and decimated the Mayans on there own with less than 20 men. The Mayans fled north to Alamo, Texas effectively ending the Mexican war for independence.
General Chimichanga gets most of the credit for winning the Mexican war for Independence on Cinco de Mayo, but Commander Nacho Cheese was the real hero. He and the Burrito Boys saved Mexico from the Mayans.
by General Chimichanga May 6, 2022
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Cinco means five and de Mayo stands for "better take a cab home gringo" because 5 times the cervesa means 10 times the hangover bro.
All beers are for a nickel, so while the mahi-mahi mango chutney tacos are good, ayeeeee! Cinco de Mayo is really turning into amatur drinking night isn't it?
by ginger petunia January 6, 2005
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