What is the Chromecast on the Xiaomi TV Box S (2nd Gen)?

Chromecast enables wireless streaming, allowing you to cast content from your smartphones, tablets, or computers to the TV. This eliminates the need for physical connections and cables.
For your reference, here are more information about Chromecast on the Xiaomi TV Box S (2nd Gen):
1. Chromecast allows you to stream a wide range of content, including movies, TV shows, music, games, from popular streaming platforms like Netflix, YouTube, Disney+, Spotify, and many others;
2. Chromecast allows for screen mirroring, letting you display the entire screen of your smartphone, tablet, or computer on the TV. This is useful for presentations, and sharing photos on a larger screen;
3. You can use voice commands through Google Assistant to control Chromecast, such as initiating content playback, pausing, or adjusting the volume.
Note: 
Your external devices also must have a built-in Chromecast feature.