What does it mean if a question is "closed"?

Why are some questions closed?

Questions that need additional work or that are not a good fit for this site may be closed by experienced community members. Closed questions cannot be answered, but can be edited to make them eligible for reopening. If your question is closed, you will receive private feedback on the reason why it was closed.

Any closed question that receives one reopen vote by a user with sufficient reputation is automatically added to a reopen queue for community review. In addition, any question with significant edits that address the close reason(s) gets added to the reopen queue. If enough community members agree, the question will be reopened and can accept answers.

These are the categories of questions that may be closed by community members with the close/reopen votes privilege. The quoted text below reflects what is shown to close voters when voting to close a question:

  • Duplicate - The fundamental goal of closing duplicate questions is to help people find the right answer by getting all of those answers in one place. There’s more information in our help center article about duplicate questions.

    This question has been asked before and already has an answer.

  • A community-specific reason (previously known as Off-topic) - Each community decides which specific topics are and are not allowed on their site. You can see this list of disallowed subjects for this site by viewing this help center article.

    This question doesn’t meet a Puzzling Stack Exchange guideline.

    If you believe the question can be reworded to fit within the scope, consider editing the question or leaving comments for improvement.

  • Needs details or clarity - Sometimes we need more information in order to help solve your problem.

    This question should include more details and clarify the problem.

    Edit your post to be more specific about what you're looking for, and be sure to address any concerns that other users brought up in the comments.

  • Needs more focus - If your question has many valid answers (but no way to determine which, if any, are correct), then it probably needs to be more focused to be successful in our format.

    This question currently includes multiple questions in one. It should focus on one problem only.

    This can often be fixed by breaking the post into multiple questions, or by focusing on a specific part of the problem.

  • Opinion-based - Discussions focused on diverse opinions can be great, but they just don't fit our format well.

    This question is likely to be answered with opinions rather than facts and citations. It should be updated so it will lead to fact-based answers.

    It’s often possible to rewrite opinion-based questions to focus on a more fact-based line of questioning. If you see a way to do this, consider editing the question.

Who can close questions?

Users with 3000 reputation can cast up to 24 close votes per day. When a question reaches 5 close votes, it is marked as being Closed, and will no longer accept answers. Users with the same privilege may also vote to reopen questions the same way. Each user may only vote to close and reopen a given question once. (For example, if you vote to close a question that is closed and then later reopened, you cannot vote to close it again.)

Moderators may close or reopen any question with a single vote without any of the restrictions mentioned above.

For more about reopening questions, see "What if I disagree with the closure of a question? How can I reopen a closed question?"