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1.
They weight gained from playing to much World of Warcraft.

Hey lets hit the gym and loose some of our WoW Weight
by Troel January 18, 2008
 
2.
WoW Weight refers to the weight you put on after excessive/prolonged periods of playing WoW; recently speaking, WoW: Cataclysm.

It's also what you would say after realizing you put on the weight; ie "WOW," due to the fact you put on so much weight from playing.
Joe: looks in mirror Holy balls! Wow!
Joe 2: What is it?

Joe: I've put on a lot of weight, geez.
Joe 2: You bought Cataclysm, right?
Joe: Yeah, so?
Joe 2: WoW weight, gg.

Jim: Man you've got a lot of food. What for?
Jim 2: Just bought Cataclysm, gonna put on some Wow Weight.
by jakesgotbigswag January 01, 2011