WTF are seller-defined audiences?

The IAB Tech Lab’s seller-defined audiences specification is one of many, many digital ad industry efforts to replace the third-party cookie with purportedly privacy-friendly alternatives. It’s effectively a cohort-based targeting method packaged with a nutrition label for the corresponding ad targeting data. 

Instead of a publisher sharing person-specific identifiers like cookie-based IDs or email addresses with advertisers, audiences are organized into groups based on categories like demographics, interests and purchase intents using IAB Tech Lab’s Audience Taxonomy standard. And advertisers can check the makeup of these seller-defined audiences by referencing the corresponding data transparency label that outlines who provided the audience data, what the audience segment is, how the segment was compiled and what the underlying data source is.