As a result, the human population tends to gather around sundown on Zombie New Year to throw large, wild parties, hoping their numbers & noise will scare the zombies away. Some people are known to get staggeringly drunk as a form of mockery against the zombie hoards.
At dawn on the Saturday following Zombie New Year, the initial zombies return to their graves, but any humans that they turned continue to walk the earth until they are put down.
It should be noted that, for reasons still unknown, an alcoholic stupor makes it harder for zombies to detect you and, if they do, makes it harder for them to turn you.
"How drunk were you?!"
I was so drunk, I didn't wake up until THIS Zombie New Year!
"Oh, shit, he's a zombie!"
Alternately it would be the date from which Zombies finally conquered the world. Many dispute this, however, stating that it would be impossible unless zombification could be passed on a microbal level. Unless zombification could be passed as such, and infect all manner of life, then technically the Zombie forces could never truly conquer the world.