Today is el Dia de los Muertos (the Day of the Dead) in Mexico. Though it roughly coincides with Halloween and has similar themes, el Dia de los Muertos is something quite different.
Think of it as a national (Mexican) acknowledgement of the inevitability of death, with a fusion of Christian and Aztec symbols and traditions.
That’s a simplistic and incomplete explanation, but it’s a start.
I was in Mexico in 1995 during the annual observance. It is something to see, especially to gringo eyes.
The above video is in Spanish. But even if your Spanish isn’t so good, you’ll get a feel for what the holiday is all about.