There are probably hundreds of different kinds of growing medium, anything that a plant can grow in is considered a growing medium. There are manmade as well as organic (natural) mediums.

The type of system you are using, what kind of crop you are growing and local environment are just some of the many determining factors involved when choosing a growing medium. There may be several mediums that will work equally well for your particular needs. Many times it boils down to availability, price or personal preference.