Updated Views is a report of general beliefs or perspectives that one has substantially changed their mind about. A post on this may share what one used to think, what the new views are, and what caused the change. Sharing such accounts publicly is prosocial and allows others to learn from one's experience too.
This tag is specifically for changes in general beliefs about the world. Retrospectives that are focused on evaluating concrete actions and projects fall under Postmortems & Retrospectives. Central examples of Updated Views posts are "'Other people are wrong' vs 'I am right'" and "Six Economics Misconceptions"; a central example of a Postmortems & Retrospectives post is "Arbital Postmortem". Posts describing broad projects leading to very general updates, such as "Three ways CFAR has changed my view of rationality", may qualify for both tags.