A flat glass that has been specially heat-treated or chemically treated to induce high compressive surface and edge stresses substantially greater than those for heat-strengthened glass. NOTE: 1) Tempered glass is not necessarily safety glass; 2) The heat or chemical treatment process significantly reduces the tendency of the glass to break under external forces or temperature changes; 3) After tempering, this type of glass cannot be cut, drilled, ground or further processed. Sandblasting, etching or other surface processing must be done before tempering.