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 the tools available for users with at least 10000 points of reputation.
5 questions
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…
11 questions
User accounts can be temporarily banned ("suspended") by ♦ moderators for violation of the site rules. Use this tag for any questions related to user suspensions.
7 questions
0 questions
28 questions
For questions concerning area51 proposals.
10 questions
Questions specifically about the process of asking questions on this site.
For questions about bonus reputation obtained when associating SE accounts.
5 questions
awarded to encourage and incentivize positive community actions within the site.
20 questions
should be used when you are expecting a large number of diverse answers to a question.
8 questions
For questions about the words and phrases which are blocked from appearing in posts or titles.
3 questions
For discussions about blacklisted tags and proposals to blacklist some tags.
5 questions
For questions about the bookmark feature (previously called favorite questions).
8 questions
a way to get additional attention for a question by offering some of your own reputation for great answers.
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.
13 questions
for questions and bug reports related to the SE chat system.
15 questions
For questions about citation helper feature.
5 questions
For questions concerning citation of posts from MO and citation of other resources when posting here.
18 questions
For questions related to closed questions (and on-hold question) and also process of closing in general.
3 questions
For questions about comment @replies
11 questions
0 questions
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.
2 questions
For questions about the user named Community ♦ present on MathOverflow (and other Stack Exchange sites.)
9 questions
A tag for questions about the community wiki feature (regardless of whether or not the questions themselves are community wiki).
19 questions
For questions about the copyrights of the Stack Exchange sites themselves or about the posting of copyrighted material by users.
11 questions
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).
14 questions
For questions related to public dumps of MathOverflow and Stack Exchange data.
5 questions
The Stack Exchange Data Explorer (SEDE) allows you to create and run queries against copies of the databases of popular Stack Exchange sites.
2 questions
For questions about user accounts that have been deleted, or the general process of account deletion.
use for any questions related answer that are deleted, or in a deleting process.
5 questions
for questions deleted from the site, or in a deleting process. The tag 'specific-question' should also be used when referencing a specific question.
32 questions