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 that have been closed as duplicates may sometimes be merged by moderators. One question is retained as a stub while all answers appear on the other.
There is no Meta Meta Mathoverflow, so questions about this very site just get this tag.
The process of migrating off-topic questions from one Stack Exchange site to another.
Reproduction of significant parts of content of MO happens on some other sites. Some of them are covered by the license others are not. Questions on both types can be asked under this tag.
Questions dealing with moderator actions, pages, abilities or decisions.
Questions about diamond (♦) moderators, their powers, and actions they have taken.
For questions about single users having multiple accounts, known as sock accounts.
For questions about MathOverflow newsletter - possibility of getting an email with top posts.
For discussions and questions on the appropriateness (for the main site) of a question or a certain type of question.
OpenId is an open standard that allows users to log in to many websites with a single set of third-party credentials.
A post ban means that a user is blocked from asking new questions, or posting new answers.
for problems and suggestions for the privileges gained by reputation on the main site and on meta.
Indicates that the post shares product or configuration change concepts during the Discovery phase. Open to receiving feedback from the Community preceding implementation.
Protected questions have the additional restriction that users with low reputation are not permitted to answer the question.
The undisclosed algorithm through which all new questions are passed to determine if they can be posted on SE.
Questions and discussions on and related to the reputation point system used on the main site.
For questions related to how the site looks, feels and behaves when its responsive design comes into play
For questions about the review queues.
For questions about the public lists of changes made to posts by a site's users. They are available for questions and answers by clicking the "edited X min ago" link, and on tag wikis as "history" and…
For questions about the various RSS feeds provided by Stack Exchange sites.
for sandbox questions, which allow people to write answers meant for testing of a particular issue, or a draft for a later answer.
A question concerning saves - a place in user's profile where various lists of questions and answers can be collected.
For questions about built-in search functionality of this site and about searching this site using external search engines.
Serial voting is the act of casting many successive upvotes or downvotes on the posts of a specific user.
Questions related to the "side bar"; the bar that runs down the right side of the page on Stack Exchange sites.