Impressions: It refers to the number of times an ad is delivered to the listener. According to industry standards, determined by server logs that show either all bytes of the podcast episode file were sent or the bytes representing the portion of the podcast episode file containing the ad file was downloaded.

CPM means cost per thousand impressions
CPM can vary depending on the specifics of your audience, the season, the podcast topic, geolocation, and so on.

The fill rate cannot always be 100% because it depends on the availability of the ad from our partners at 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. Boost your revenue share by 10% by driving your audience through Spreaker and every download coming from Spreaker website, mobile app, or widget will give a boost of 10% on your revenue share