It just means "new video games that come on a physical disc." The 20% discount doesn't apply to gaming accessories or to digital downloads. And pre-owned games have a different discount percentage (10%).
To discourage resellers, the 20% is only valid for up to 3 copies of the same game.
So if you tried to buy 4 copies of Madden 15, you'd only receive 20% off 3 of them, and the 4th one would be charged at normal price.
You can view the full terms and conditions here:
http://www.bestbuy.com/site/global-p...at341800050017