Some TVs have a feature called Miracast. This only works with some Android devices. iPhone and iPad don't support Miracast. The icon you see in apps looks very similar to the Chromecast/casting icon unfortunately.
Some TVs have AirPlay built-in. This only works with iPhone, iPad and Mac devices. You'll see a TV with an upward facing triangle at the bottom if the app supports AirPlay.
Chromecast is a separate media streaming device you connect to a TV. This works with Android, iPhone and iPad devices, using Chromecast supported apps or casting a Chrome browser tab from a computer.
Some TVs have Chromecast built-in, meaning you don't need to buy a separate Chromecast. This works with Android, iPhone and iPad devices, using Chromecast supported apps or casting a Chrome browser tab from a computer.
Probably a longer answer than you were looking for, but it really does depend on what device you're using to share content, what brand and model of TV you have, and what technology you're looking to use to share the content (listed above).
