The biosphere is the zone of air, land and water where organisms exist. It is commonly known as the global sum of all ecosystems and consists of several layers including the atmosphere, the lithosphere and the hydrosphere.
In environmental sciences, scientists will discuss the different areas of the earth and they divided up into the atmosphere, Lithosphere and Hydrosphere which really are really confusing ideas. But ultimately they're just air, the land and the water.
Now when people started getting into ecology and starting that more, they came up with a new term called the Biosphere. And that's the overlapping areas and regions of these three where you find living organisms. Whether it's the areas of the oceans where whales and fish and other things swim or the area of the atmosphere where birds are flying and you'll find seeds flowing in the air currents or deep in the earth where you'll find cave dwelling, fish and weird fungi and other things. So that's the biosphere.