a person that plays video games 24/7

Defined by the Bungie game company as "someone who has mastered Marathon to its fullest", Marathon being a very old (in game terms) first-person shooter released by that company. A vidmaster must play on the hardest difficulty level, never shoot when he (or she) could use grenades, never use the caps lock as a "run" key, and never, EVER leave a single Bob alive. The "vid" refers to the recording the player makes of their actions in the game that proves their skills.