A vanity metric on social media platforms is a statistic that may look like a positive indicator of performance but doesn’t actually provide you with valuable insights.
they are not a valuable indicator of lower-funnel success from a revenue or business standpoint (i.e. follows, likes, comments).
Impressions are a classic example as they are often larger than reach, but only tell you how many times people scrolled past a post in their feed without revealing the bigger picture of how popular or engaging the post was.