Channels & programmatic
SSP (supply-side platform)
An SSP is the publisher-side counterpart to a DSP: the technology publishers use to make their ad inventory available to programmatic buyers, manage floor prices and connect to exchanges. Buyers rarely touch SSPs directly, but supply-path choices affect cost and quality.
In practice
The same impression can often be reached through multiple SSP paths at different effective costs - the reason supply-path optimisation exists.
For planners, the practical takeaway is that 'programmatic' is a chain of intermediaries, each taking a margin, between budget and publisher.