The tutorial pages on the official Microsoft website show how to use features on the Xbox 360. Seems normal until you look closely at two pages that say X8. On the playing games page, it says, “Play a Game (includes X8)”, and on the music page, it says, "Listen to Music (includes X8)". This would mean that the tutorial applies to the X8 console and the Xbox 360.
X8 is not that silly of a name, considering they have Windows 8 and their phone Windows Phone 8 OS. The 8 can be turned sideways and that resembles an infinity symbol, which means it could also be called Xbox Infinity. As of now, this is a rumor, and we will have to wait to see if this is going to be the official name of the next Microsoft console.
I did some research on Xbox.com and I found theses:
Play a Game (includes X8)
Listen to Music (includes X8)