A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.
Questions about diamond (♦) moderators, their powers, and actions they have taken.
A tag for questions about the community wiki feature (regardless of whether or not the questions themselves are community wiki).
no Meta Meta Mathoverflow, so questions about this very site just get this tag.
For questions concerning using images in questions, image hosting, etc.
Cross posting refers to posting the same, or almost the same, question (or post) on different sites in the Stack Exchange network (or possibly also elsewhere).
Some changes to questions, such as edits or receiving new answers, will "bump" them back onto the site's front page where the changes can be vetted by other users.
For questions on usage of links at MathOverflow (both links to various parts of this site and to other sites).
the answer the question owner thought best met their needs. Accepting is encouraged but never required. This tag is for *discussing* issues related to accepted answers, not indi…
For issues regarding the help center of MathOverflow.
Questions about suspected user spam, the spam flag or combating spam as a community
For questions about the favorite question feature or the favorite tags feature.
For questions about Markdown, a lightweight markup language used across the entire Stack Exchange network for post formatting.
Users without full edit privileges can suggest edits to posts and tag wikis
For questions about the copyrights of the Stack Exchange sites themselves or about the posting of copyrighted material by users.
For questions about comment @replies
For questions about the user named Community ♦ present on MathOverflow (and other Stack Exchange sites.)
should be used when you are expecting a large number of diverse answers to a question.
for problems and suggestions for the privileges gained by reputation on the main site and on meta.