The proportion of people who see your messaging (on any platform), and who take the action the messaging is suggesting, such as purchasing something, subscribing to a service, or even just clicking a link in the ad. For example, if you send out 100 emails and get 5 new customers from it, your conversion rate would be 5%.
An ETL Pipeline refers to the process in computing where data is extracted (E), transformed (T), and loaded (L) into an output data container.