Impressions: It refers to the number of times an ad is fetched and listened. Each time an ad is served on your content, an impression will be counted.
CPM means cost per thousand impressions i.e. ad listens.
CPM can vary depending on the specifics of your audience, the season, the podcast topic, geolocation and so on.
Fill rate cannot always be 100% because it depends on the ads availability from our partners in a specific moment. Sometimes a slot cannot be filled and that's one of the reasons why revenue can vary from one day to another.
Revenue: the amount of money you earn with the impressions reached. Every time an ad gets an impression you’ll get a 60% share.