This is simply a layer in the stratosphere containing a relatively high concentration of ozone. The earth’s atmosphere is divided into several layers, and each layer plays an important role. The first region extending about 10-12km upwards from the earth’s surface is called the troposphere. Many human activities like mountain climbing, gas balloons and smaller aircrafts operate within this region.
The next layer, extending about 12-60 km is called the stratosphere. The ozone layer is mainly found in the lower portion of the stratosphere from approximately 20 to 30 kilometres (12 to 19 mi) above the earth, though the thickness varies seasonally and geographically. The ozone layer protects the earth from the suns UV Rays by providing a filtering ability.
Above the troposphere is the mesosphere, extending about 50-85km above the surface of the earth, and then the Thermosphere, also extending about 85-600km above the earth’s surface.