An SSP (Supply-Side Platform) is a platform that allows display inventory providers (e.g. web publishers, advertising networks…) to maximise their sales by automatically managing their ad inventory on multiple ad exchanges through a single platform. It is mainly used to sell display advertising space in an automated and granular way, through RTB (Real-Time Bidding).
SSPs are the mirror platforms of DSPs on the publisher side.
Examples: RubiconProject, Pubmatic