Something that's supposed to be so important that it literally changes the way things are done. Usually, it's only important to one person and they proudly exclaim it to be a game changer, immediately rendering it retarded.
This AOL is going to be a game changer. People can log onto the interwebs at 56k and download porno movies on their home computer in less than a week!
In action... http://twitter.com/JasonCalacanis/status/2076355226Actually, this definition sucks. Let me add my own. You can also share "game changer" with a friend or share it on Twitter.