A post ban means that a user is blocked from asking new questions, or posting new answers.
A post ban is an automated ban (unlike an account suspension which is a manual temporary penalty). ♦ moderators cannot remove this type of ban.
Error messages that are produced when attempting to create a new question or post a new answer when banned in this way are:
You can't post new questions right now
Sorry, we are no longer accepting questions from your account because most of your questions need improvement or are out of scope for this site.
And, for answers:
Sorry, we are no longer accepting questions/answers from your account because most of your answers need improvement or do not sufficiently answer the question.
For more information about question and answer bans, including how to become unbanned, see the community-curated FAQ.