A unique cookie is a browser. Each browser (mobile apps are counted even though it says web only) opened is a unique cookie. So if someone opens up chrome and watches 15 videos, it counts as 15 views, but only 1 unique cookie. If someone uses more than one browser, each browser opened would count as a unique cookie. By tracking the number of views you get per day compared with unique cookies, you can estimate how many videos each viewer watches. On a given day, if you have 100k views and 25k unique cookies, each person watched 4 of your videos that day. If your ratio is closer to 1:1, then you need to work on your audience development and implement a few changes to get each person to watch more than one video during their viewing session.