Impressions represent how many times your ad was rendered on a user's screen. An impression does not necessarily mean the user saw or paid attention to the ad. Impressions are the basis for calculating CTR and CPM, and are most relevant in awareness campaigns.
A Display campaign generated 500,000 impressions and 2,500 clicks, resulting in a 0.5% CTR — considered good for Display Ads. Total cost was EUR 750, meaning a CPM of EUR 1.50.