What does the Impressions mean in Google Analytics?

 page impressions are the number of times your site came up during a search.

Clicks are the number of times someone clicked on your page during search and converted to visitors.

Click through rate is the ratio of impressions and clicks.

An impression is counted each time your ad is shown on a search result page or other site on the Google Network.

An impression is counted each time your ad is shown on a search result page or other site on the Google Network. Each time your ad appears on Google or the Google Network, it's counted as one impression. In some cases, only a section of your ad may be shown.