What does "impression",“Allocation” and "filled rate" mean?

• Impression:

Sometimes called a view or an ad view, is a term that refers to the point in which an ad is viewed once by a visitor, or displayed/heard once on a web page/radio. The number of impressions of an advertisement is determined by the number of times the page/spot is located and heard.

• Allocation: 

In the media, advertising, and marketing industries, advertising inventory or allocations is the space available to advertisers on newspapers, magazines, and digital platforms.

For instance, if you trigger a 2min file, there is a potential of four 30 seconds ad spots, the inventory or allocations = 4, however we might only have 3 ads available to fill the ad-break, consequently impressions=3 and filled rate = 75%

• Filled Rate:

The number of times an ad was shown to users (impressions) compared to the number of times an ad was requested from a specific ad source (allocation).

The fill rate for each ad source is calculated using the following formula:

 Impressions / Allocations