What is impressions?
Impressions
The total number of times a post was displayed, counting repeat views by the same account.
Impressions rise with time in feed and with sharing, so a post that keeps circulating accumulates impressions long after publication. Comparing impressions to reach tells you how often the average viewer came back.
Like reach, impressions are a first-party metric: they come from Instagram Insights on the account that published the post, and are not visible to anyone outside it.