Impressions count how many times a post, profile, story, or ad was displayed.
One person can generate multiple impressions if they see the same content more than once.
Impressions are useful for understanding visibility, but they do not necessarily mean people clicked, watched, or engaged.
Impressions are useful for measuring exposure and frequency, but they should be paired with reach or engagement to understand whether visibility is concentrated or broad.
Reach counts unique people, impressions count total displays. If one person sees a post three times, that is one reach and three impressions.
Because people are seeing the content more than once. A large gap between impressions and reach means high frequency, which can be good for recall or a sign of a small audience seeing the same post repeatedly.
They can be if reported alone. Impressions become useful when paired with reach, engagement, or clicks, because those show whether the visibility actually did anything.