What is the circle with grid and how can I disable It?

I am not able to press any icons or restart the phone. My kids activated it while playing with it and now I am stuck. I could not do the normal restart so had to hard restart the phone as per this link(https://www.youtube.com/watch?v=KhLgef8Rsq8&t=98s) and now phone is working fine. Hope it helps someone.https://www.youtube.com/watch?v=KhLgef8Rsq8