This video from Valve introduces the Steam Link, and how it will enable playing games from your Steam library streamed to any television in your home when it's released next month. Here's a reminder of how this works from the Steam Link page.

Simplicity
Setup is easy. Just connect your Steam Link to your TV and home network. It will automatically discover any computer running Steam on the same network.

All that’s left to do is grab your Steam Controller, kick back and enjoy your gaming rig from the comfort of your couch.

Performance
Steam Link is designed to take advantage of the horsepower you already have in your home, streaming from your current gaming computer. Video and audio data is sent from your computer and controller input is sent back in realtime.

Virtually every game that your PC runs can be played over Steam Link.