In other words, you can remote play games from another, more capable PC on your local network. Steam will detect the same login and the rest is apparently magic.
Read on for the announcement, and stop by the site for more info.
In-Home Streaming, a new feature of Steam, is now released to all users. Players who have multiple computers at home can immediately take advantage of the new feature. When you login to Steam on two computers on the same network, they automatically connect, allowing you to remotely install, launch, and play games as though you were sitting at the remote PC.
Steam In-Home Streaming allows you to play your PC games on a lower-end computer, such as a laptop or home theater PC, or a computer running another operating system, such as Mac OS X, SteamOS, or Linux.
When you play a game using In-Home Streaming, video and audio are sent through your home network from your high-end gaming PC to another device in your home. From here, your keyboard, mouse, and controller input is sent back to the remote computer.
For more information, please visit http://steampowered.com/