Reverse ETL

Reverse ETL is the reverse flow of data: instead of pulling data into a warehouse for analysis, it pushes processed data from the warehouse back out to operational tools (ads, CRM, email) to be acted on.

If ETL brings data in to understand it, reverse ETL takes that understanding back out to act on it; a cohort or segment you built in the warehouse goes to a destination that actually does something with it. It is the bridge between analysis and execution and is exactly what makes cohort sync possible. But it has two serious obstacles. First, privacy: sending user data (even hashed) to a third-party tool is a data sharing that needs a legal basis and consent. Second, ecosystem dependence: reverse ETL usually makes sense with global destinations (ad and marketing platforms), and for a business not tied to that ecosystem, or one keeping data inside the border, its usefulness is limited.