Impressions not resulting in Clicks
You may see multiple imprsssions in your Google Search Console reports that do not result is many or any clicks. This may mean that the Internet user did not find what they were searching for on your page that resulted in an Impression or it could mean that you need to adjust the content to hopefully "capture" a Click.
In my case I am seeing a lot of impressions for "where Lovejoy was filmed" and I get a fair amount of clicks from them. However, it not reslly what this website is all about.
The converse of this is where you see Clicks but there were no Impressions reported in your GSC reports. This is more difficult to understand, whereas the failure to get a visitor to click on your page is more a question of that your content is not compelling enough.
Impressions and Queries
In your Google Search Console reports an Impression is an indication that your page has been listed in a search result.
It is also possible to get Impressions with no Queries and Clicks with no Impressions.