Hot meta posts are the posts which can be found in (the corresponding section of) the community bulletin. The main criteria for selection can be briefly summarized as: The question is tagged discussion, it has score at least $+3$ and it is at most 14 days old. There are also some further details, you can find the complete explanation in the corresponding FAQ ...


I think that the reason that "Hot Meta Posts" exists is that the Meta needs more attention than the main site (for obvious reasons). Since the main site gets much more visibility, there is no need for an extra box calling attention to it.

Only top voted, non community-wiki answers of a minimum length are eligible