Impressions
Total number of times your post was shown, including repeat views.
Impressions count every load of your content, including the same user scrolling back. They're inflated relative to reach. When you see a post with 10k impressions but only 4k reach, that means each viewer saw it ~2.5 times on average. High impression-to-reach ratios usually indicate the algorithm is showing your post repeatedly in the same feeds (common for boosted posts or evergreen content the algorithm recycles).