How can a post be deleted?
By a user:
You can typically delete your own posts at will; for exceptions, see "When can't I delete my own post?" below. To delete a post, just use the "delete" link below it.
Moderators can delete any post instantly.
Users with reputation >= 10k (more precisely, the “moderator tools” privilege; 2k on beta sites) can vote to delete questions that have been closed/on-hold for 48 hours. It takes three votes to delete; more if the question is popular, but ten votes at most.
Users with reputation >= 20k (more precisely, the “trusted user” privilege; 4k on beta sites) are not subject to the 48-hour waiting period for deleting closed questions with a score of -3 or lower. They may also delete answers of score -1 or lower. It takes three votes to delete an answer.
Six users with reputation >= 2k (more precisely, the “Edit Questions And Answers” privilege; 1k on beta sites) can cause automatic deletion of a post if they choose "recommend deletion" from within the low quality review queue.
By the system:
The system will automatically delete any post flagged six times as offensive or spam.
The system will automatically delete closed (not as a duplicate), unlocked questions with zero or negative score having no upvoted or accepted answers or pending reopen votes, that were closed 9 or more days ago and haven't been edited in the past 9 days.
The system will automatically delete unlocked, unanswered questions that have negative score after 30 days.
The system will automatically delete unlocked, unanswered questions with score of zero (or one if the owner is deleted), fewer than 1.5 views per day on average, and fewer than two comments after 365 days.
The system will automatically delete any question (and its answers) or answer with a score less than 0 when its owner's account is deleted.
The system will automatically delete questions migrated to other sites after 30 days. Note that this applies only for the original question created on the original site (the "migration stub"), not the question newly created on the other site as a result of the migration. Questions autodeleted under this criterion still have their revision histories visible to everyone, and links to them redirect to the new question instead of showing an error page.
Questions and answers that receive six "Recommend Deletion" reviews in the Low Quality Posts review queue are automatically deleted "in review". Posts can be kicked into this queue either automatically or if particular flags are cast on them (very low quality flags on questions and the very low quality & not an answer flags on answers), and can be removed from the queue if enough "Looks Good" reviews are cast against them.
When can't I delete my own post?
You can't delete answers that have been accepted.
You can't delete any question that:
- has an upvoted answer, or
- has multiple answers (even if there are no upvotes)
You can't delete any of your questions or answers if you haven't registered your account (that is, associated an OpenID with it).
Can I see a list of my deleted posts?
Yes, but only posts deleted in the last 60 days. Full list of deleted posted won't likely happen.
How can I undelete one of my posts?
Self-deleted posts can be viewed and undeleted by their original authors. However, self-deleted questions cannot be edited by their authors unless undeleted first. Self-deleted answers can be edited by the author without undeleting. Normally, if your deleted post is not self-deleted, you can't undelete it yourself (though you may be able to vote to undelete). An exception: if an answer is deleted from Low Quality review queue by "Recommend Deletion" votes, without three trusted users voting to delete, then it can be undeleted by the author.
If your post was deleted by trusted users, it will require three undelete votes to be undeleted - politely asking for this on Meta may attract the necessary votes if you make a good case for why the question should be restored.
If your post was deleted by a moderator, you can flag one of your other posts and write a note in the "other" section explaining the situation and requesting undeletion.
Note: deleted questions do not appear in search results, so you if you wish to later undelete a question that you've deleted you must have saved the URL somewhere. Users with 10K reputation and up can also mark questions as a "favorite" and find them later from the Favorites tab on their profiles. Only moderators can search for deleted posts, not non-moderator 10k+ users.
Deleted posts that are no more than 60 days old (since the creation date) are listed under "recent deleted questions" or "recent deleted answers".
What does deletion mean for a post?
Deleted posts are usually not physically deleted (that is, removed from the system); they're just hidden (AKA soft-deleted). This means they won't appear in search results or data dumps, and normal users following links to them will see a 404 (not found) page.
Moderators, and normal users with >=10k reputation, see all deleted posts. Moderators are able to undelete any deleted post.
"10k users" may vote to undelete deleted questions: it usually takes three votes to undelete a question, but sometimes more.
"20k users" may also vote to undelete deleted answers: it takes three votes to undelete an answer.
What else should I know about deleted posts?
Reputation changes from bounties and votes (both up and down) on deleted posts (including answers to a deleted question) are nullified. (Exception: Reputation earned for posts with a score of three or higher, and where the post has been visible on the site for at least 60 days, is retained).
Reputation lost as a penalty for having a post deleted by flagging is not returned.
The first time you delete your own post that has a score of three or higher, you will earn a Disciplined badge.
The first time you delete your own post that has a score of negative three or lower, you will earn a Peer Pressure badge.
Answers are automatically deleted when the question they're attached to is deleted. Such answers are automatically undeleted when the question is undeleted, except for answers that were deleted before the question was deleted.
How do votes to delete work?
What are the criteria for deletion?
For questions, a post that no longer adds anything to the site should be deleted. Basically, this includes most closed questions that cannot be improved and reopened. However, it may be beneficial to keep duplicates to aid future users in finding the canonical question.
For answers, any post that is not an answer (should be a comment, doesn't answer the question, etc.) should be deleted. Answers that are wrong or that dispense poor advice should be downvoted, not deleted.