Best definition
A party centered around the Nintendo Wii gaming system. A combination of the words “Wii” and “Fiesta”.

Niko: Dude I totally just got Super Smash Brothers Brawl. We should totally have a Wiiesta!

Steve: Dude, you’re so gay.

Wiiesta: define #2
A party involving one or more Nintendo Wiis, and possibly mexican food.
“Dude, this weekend we should bust out the Wiisports and tacos and have ourselves a Wiiesta!”