Glossary · Platforms and measurement
SSP
Supply-Side Platform: a platform a site or app uses to sell its ad space.
In detail
An SSP (supply-side platform) is the tool of whoever has space to sell: a publisher, a blog, an app. It offers those spaces to many buyers at once, including DSPs, and accepts the best bid.
For people who produce banners, the SSP matters because it can add its own checks before accepting an ad.
Example
A digital newspaper puts its 300×250 spaces on an SSP and DSPs bid on each impression.