If you recall your science lessons from school, you know that the earth is surrounded by several layers of air called the atmosphere, as do the other planets in the solar system. It is what allows us to breathe; it lets breathable air circulate within the boundaries it creates and even protects us from objects which may fall from outer space.
The layers include: troposphere, stratosphere, mesosphere, thermosphere and exosphere. The ionosphere is comprised of the outer portion of the mesosphere, thermosphere and exosphere and it is so named because it is composed of plasma, meaning it is ionized by radiation from the sun.
Ionization is the process in which negative free electrons escape from the atoms or molecules originally containing them, and the opposite process, called recombination, is when photons are released from atoms or molecules because of captured free electrons.
The balance between ionization and recombination determines ionosphere ionization. What does this have to do with you? It plays a very important role in radio propagation: the ionosphere is the reason we can communicate with people from the other side of the globe through radio waves.