https://www.theverge.com/2017/9/12/16290210/new-iphone-emoji-animated-animoji-apple-ios-11-update

Apple is introducing a new Animoji feature in iOS 11, which are animated versions of the popular emoji found on the iPhone. Animoji will use the Face ID hardware face-scanning features of the iPhone X to create custom 3D versions based on your own facial expressions.

Animoji will be available directly within the Messages app for iOS 11, and it will be able to immediately pick up facial expressions and animate accordingly. You can edit emoji in fullscreen, and they’re all animated in real-time before you send them as a message. Recipients will receive them as looping videos with audio, and they look like they’ll be a lot of fun to send and receive.