What it means
Impressions count how often an ad or product was displayed — regardless of whether it was noticed or clicked. They are the base metric for reach and an early indicator of whether targeting and bids work: too few impressions point to bids that are too low, overly restrictive keywords, or weak relevance. Amazon additionally distinguishes viewable impressions: counted only when at least 50% of the ad was visible for a minimum duration (image: 1 second, video: 2 seconds) — relevant especially for vCPM campaigns and for evaluating placements.