What does "tempered glass" refer to?

Tempered glass refers specifically to glass that has been heat-treated to increase its strength and safety properties. The tempering process involves heating the glass to a high temperature, then cooling it rapidly. This process strengthens the glass, making it up to five times more resistant to breakage compared to regular glass of the same thickness.

In the event that tempered glass does break, it is designed to shatter into small, blunt pieces rather than sharp shards. This characteristic significantly reduces the risk of injury, making tempered glass a popular choice for various applications, including shower doors, glass doors and tables, and storefronts.

The other options do not accurately describe tempered glass. Opaque glass does not allow light to pass through, while thin glass that shatters easily does not possess the strength or safety features associated with tempered glass. Lastly, chemically treated glass refers to a different type of glass that is treated to resist scratches, not to increase strength through heating. Thus, the choice that describes tempered glass accurately is the one involving heat treatment, enhanced strength, and safe shattering properties.