Toughened glass or tempered glass is heat treated glass which has been warmed up and cooled of quickly. This process strengtens the tempered glass amongst five times compared to regular glass. For heat strenghtened glass the fragmentation if it breaks is different, the smaller pieces are less dangerous for injurys.
Toughened glass is often called safety glass.
Polish, cutting, holes etc has to be done before heat treatment of glass. After glass is toughened it can not be worked any more.