Glossary
Impression
One display of a post on someone's screen. The same person seeing a post twice counts as two impressions.
Also called: impressions, views
An impression is counted each time a post is shown. LinkedIn defines impressions as the “number of times your post was shown on LinkedIn”, and separately reports members reached, the “number of distinct members and Pages that saw your post”, which “does not include repeat views” (LinkedIn Help). The difference between the two numbers is repeat display to the same people.
Impressions are the widest and least informative number in post analytics. A post shown to many people who scrolled past it has plenty of impressions and did nothing. They are most useful as the denominator: engagement divided by impressions tells you whether the people who saw the post cared.
LinkedIn notes that its impression figures are estimates. Other networks use similar words with their own definitions, so comparing impressions across networks tells you less than it seems to.