Impressions are another one of those online metrics. This one is really simple though, each time your advertisement is displayed on a webpage, it counts as an impression. It doesn’t necessarily mean that the customer sees your ad or clicks on it though. It’s just a measure that the ad has been displayed.
For example…
Kira has just started a 3D printing business and she wants to advertise her services online. She uses Google AdWords to run her advertising campaign. After one week of the campaign running, she discovers that the number of impressions on her ad is low being just around 1000. After a few tweaks to the campaign and another week later, she finds that the number of impressions on her ad has jumped to 8000. A healthy number indeed!