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1.
Something we never get in Computer Applications.
"Today I tried to play a game, but Evan turned off my computer. He said, "this is not gameday."
by Evan January 18, 2005
 
2.
The art of setting donkey work and all other tedious work aside to browse the internet, draw on, and partake in the event of playing games, or game-like activities.
Frank, "Yo Evan, wanna get a taco out after school?"

Evan, "No, it's gameday!"
by Various sources January 20, 2005
 
3.
The day when you seriously get beat down by some guy who is worse then you years. This is the day of reckoning when you realize your a worthless piece of crap.
Gameday is when French-Canadians take over the world.
by Lifter November 24, 2003