Steam Link is a product and service by Valve that enables users to stream their Steam games from their PC to other devices. It originally referred to a physical set-top box that connected to a television, but now it primarily refers to the software application that can be installed on various devices such as smartphones, tablets, and smart TVs. The service allows for gameplay on these devices using a compatible controller, with the games being processed on the user's PC and the video and audio being streamed to the device over a local network.