If your post shows up on 1,000 screens, that's 1,000 impressions — whether anyone clicked or not. Impressions simply measure visibility. It doesn't matter if the person engaged with your content; just appearing on their screen counts as one impression. The same person seeing your ad three times counts as three impressions.
High impressions with low engagement means people are seeing your content but not caring about it. However, impressions are the essential first step — you can't get clicks without views first. For brand awareness campaigns especially, maximizing impressions is the primary goal. Think of impressions as planting seeds — the more people who see your brand, the higher the chance someone will eventually convert.