What is Chromecast?

Chromecast (now Google Cast built into Google TV devices and many smart TVs) lets your phone send video to the TV: tap the cast icon in YouTube, Netflix or Spotify and playback jumps to the big screen.

The phone is only the remote — the TV streams directly from the internet, so the phone can leave the room. Both devices must be on the same Wi-Fi network, the usual culprit when the cast icon disappears.