Supply-Side Platforms (SSPs) are advertising-technology platforms used to sell a publisher’s ad space in an automated fashion, typically via Real-Time Bidding (RTB) auctions.
SSPs are most often used by online publishers (websites and apps) to help them obtain the most yield possible from their display, video, mobile, and native ad inventory.
In order to sell this available ad space, a supply-side platform (SSP) connects with multiple ad exchanges and networks, which in turn offer the inventory to advertisers via demand-side platforms (DSPs).