https://techcrunch.com/2019/04/16/apple-could-build-macos-feature-to-use-your-ipad-as-extra-mac-display/

According to a report from 9to5mac’s Guilherme Rambo, Apple is working on a feature that would let you pair your iPad with your Mac to turn your iPad into a secondary Mac display. That feature codenamed Sidecar could ship with macOS 10.15 this fall.

If you’ve been using Luna Display or Duet Display, you’re already quite familiar with this setup. Those third-party hardware and software solutions let you turn your iPad into an external display. You can then extend your Mac display, move windows to your iPad and use your iPad like an external display.