In Google Search Console, an impression is counted each time a link to your site appears in a Google result that someone saw, or could have seen.
An impression, in Google Search Console, is a time a link to your site appeared in Google's results. Google counts it when a searcher "has seen (or potentially seen)" the link. On an ordinary results page, being on the page is enough; in a carousel, the link has to be scrolled into view.
So impressions measure how often Google offered your page, not how often someone read your result. A page at position 9 collects impressions from many searches where nobody scrolled that far.
For a new site, impressions are the first sign Google has started showing your pages. What they mean next to clicks and position is in what impressions, clicks and position mean. See also click-through rate.