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.
For questions about the copyrights of the StackExchange sites themselves or about the posting of copyrighted material by users.
For questions about, well, questions: how to ask, whether specific questions are appropriate, and so forth.
Per-site lists of tags that cannot be created.
a text which is hidden until you move cursor above it. It might be useful when for separating full solution from a hint.
For issues with how Stack Exchange sites look or work that are specific to Google's Chrome browser.
From Oxford Dictionaries, paraphrasing to suit the needs of *this site*: "A website or web page on which (in our case) M.SE records opinions, links to other sites, etc. on a regular basis".
For questions about the mobile versions of Stack Exchange sites. For questions about the mobile apps, use the [android-app] and the [ios-app] tags as needed.
to be used for the Official Stack Exchange application only. The app is available in the App Store, for iOS 7 on iPhones only. When posting bug reports, please specify the app's version.
For questions about single users having multiple accounts.
the percentage of questions for which the user has accepted an answer.
for questions involving the 'Front Page' - the list of top questions with activity
Questions about the "hot questions list" which appears on the main page and truncated on all pages in the SE network, as well as its effect on Math SE.
fetched and displayed on the Stack Exchange network. This is not for general Gravatar support inquiries.
The undisclosed algorithm through which all new questions are passed to determine if they can be posted on SE.
For questions about various userscripts and bookmarklets.
a process which helps cleaning the site by deleting some questions. Criteria for auto-deletion are based on low score and age of the question.
For questions and requests to merge multiple Stack Exchange accounts of the same user.
the act of temporarily blocking the account of a specific user.
Locking a question prevents answering, editing, commenting, voting, closing, and reopening. Answers must be locked separately and may still be voted upon. Only diamond moderators may lock posts.
For every user, the reputation from the main site is shown on meta. However scores of the posts on meta are still stored, so it is possible to obtain reputation-based badges on meta (mortarboard, tag …
for questions about the CSS styles used in Marthematics SE.
When your question gets the community to have a vote
General questions about users and user accounts.
a user-generated list of related questions shown when viewing a question. Its content comes from questions that users have linked in the question, their answers, or i…
websites copying content from other websites. Use this tag for questions related to sites copying contents from math.SE. (In particular, if this is done without proper attribution.)
"The Dupehammer" refers to the ability of tag gold badge owners to unilaterally close and reopen duplicates which were asked in tags of which they have a golden badge.
For questions regarding the badge tracking functionality in the user profile area.