What are Multi Window apps?
Multi-window mode enables multiple apps to share the same screen simultaneously. Apps can be side by side or one above the other (split-screen mode), one app in a small window overlaying other apps (picture-in-picture mode), or individual apps in separate movable, resizable windows (free-form mode).
What is multi window UI?
The Android Multi Window function allows you to open and use two apps simultaneously by splitting the screen view.