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.
for questions on Meta that relate to a specific answer on MathOverflow. (If a linked answer serves only as an example of a more general issue you want to discuss, this tag should not be u…
Protected questions have the additional restriction that users with low reputation are not permitted to answer the question.
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.
For questions about MathOverflow newsletter - possibility of getting an email with top posts.
For questions involving the "Ignored Tags" specified in a user's Preferences. Questions with these tags are dimmed or removed entirely from question lists.
a user-generated list of related questions shown in the sidebar when viewing a question. Its content comes from questions that users have linked in the question, thei…
the block of links that appears near the top of the right-hand sidebar on most pages, consisting of featured posts, events, blog entries, and hot meta posts.
For questions about exporting and printing MathOverflow posts.
For questions about various userscripts and bookmarklets.
For questions related to how the site looks, feels and behaves when its responsive design comes into play
The undisclosed algorithm through which all new questions are passed to determine if they can be posted on SE.