Final Answer:
The report that shows how long a video was watched in aggregate is typically known as a "Watch Time" report.
Step-by-step explanation:
A "Watch Time" report provides insights into the total duration of time that viewers spent watching a video or a set of videos. This metric is crucial for content creators and platform administrators to understand audience engagement and the popularity of specific video content. The report aggregates the total watch time across all viewers, offering valuable data on the overall performance of videos. It helps creators identify which videos are capturing and retaining audience attention. This type of analytical information is essential for making informed decisions about content creation, audience preferences, and overall video strategy.
The answer is "Watch Time" report.