What is a Supply Side Platform?
A Supply Side Platform (SSP), sometimes referred to as a Sell Side Platform, is the technology that allows publishers to automate the ad selling, managing, and optimizing processes.
Before SSPs were invented, publishers had to manually manage and sell their ad inventory. This was extremely difficult to do efficiently and made it impossible for publishers to scale their ad-selling operations. Fortunately, SSPs now exist to streamline this procedure.
In a nutshell, SSPs connect publishers to demand sources—think ad networks, ad exchanges, and demand side platforms (the opposite of supply side platforms.)
App mediation is one example of a supply side platform, though there are others as well.