1. A region in the upper atmosphere, about 6–30 miles (10–50 kilometers) high, with significant concentrations of ozone, formed by the effect of solar ultraviolet (UV) radiation on oxygen and also present in trace quantities elsewhere in earth's atmosphere.
2. The layer of the upper atmosphere, from 15 to 50 kilometers (10 to 30 miles) above the earth's surface, where most atmospheric ozone collects, absorbing harmful ultraviolet radiation from the sun.

In the 1980's it was realized that industrial pollutants such as CFC's were damaging the ozone layer and that holes had appeared in it, especially over the Antarctic.

CFC refers to a gas containing carbon, hydrogen, chlorine, and fluorine; some forms of which are said to damage the ozone layer in the earth's atmosphere.