What is System UI for Android phones?

Related questions

1. What UI developer should know?
2. What is the UI developer?
3. How do I become a UI developer?
4. What is UI design patterns?
5. What is the purpose of UI?
6. What are UI technologies?
7. What's the importance of user interface UI in mobile application development?
8. What are UX principles?
9. What are UI controls?
10. Which is the best user interface for Android?

Tags

1. #tuner
2. #battery
3. #sweet
4. #called
5. #google
6. #little
7. #icons
8. #percentage
9. #packs
10. #status
11. #system
12. #marshmallow
13. #introduced
14. #android
15. #showing
16. #tweaks
17. #hidden
18. #hiding