Reverse ETL Definition
ETL and ELT both transfer data from third party systems, such as business applications (Hubspot, Salesforce) and databases (Oracle, MySQL), into target data warehouses.
But with reverse ETL, the data warehouse is the source, rather than the target. The target is a third party system.
In reverse ETL, data is extracted from the data warehouse, transformed inside the warehouse to meet the data formatting requirements of the third party system, and then loaded into the third party system for action taking.