The total number of ad requests seen by each ad network. Some of these requests may be counted more than once as the request moves through the mediation stack – Total requests
The total number of unique attempts to request an ad. This number doesn’t count the same request multiple times. Instead, each request is only counted once, no matter how many networks receive that request as it moves through the mediation stack – Unique requests
This question is from the Check your Knowledge section of the “Use the mediation report” lesson from the “Grow Revenue with AdMob Mediation” unit which is a part of the Get Started with Google AdMob course.