Assuming you want to know, the Nvidia Shield is a set-top box that runs Android TV as it's operating system, and is fairly game focused in it's purpose (though it can also playback media and do a lot of other stuff).

Gamestream is software that allows users to stream games from a PC to an Nvidia Shield. It allows people to keep their powerful gaming PC set up at a desk, while also being able to play sitting on their couch in the living room. (And may also be able to stream across the internet, I'm not sure. I don't have a shield, but Steam's equivalent software can work remotely, though it takes mighty good internet to be able to get it to work smoothly.)