Tempered glass is a hardened glass, specially designed to cover and protect the mobile screen from scratches and other damages. It does not affect the screen's functionality. In case the mobile falls, it does not guarantee that the screen will not break along with it, but it provides extra protection.
It has adhesive on the entire surface, unlike edge glue protectors that have adhesive only on their perimeter. This helps in better fitting and smooth operation of the touch screen. Also, it prevents dust from passing underneath, which can happen with edge glue protectors when the perimeter adhesive wears off.