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.

designed to solicit opinions, influence site policy, or debate a particular topic, with the goal of reaching a community consensus.
A request for assistance from community, moderators, or staff with one of the site's features
Bug reports marked resolved or feature requests filed as done and live.
650 questions
Something amiss or broken with how you're working with the site? Report it.
You have an idea for a new feature, or for a change to the existing functionality.
asking to have some questions retagged, usually for a misused tag, or generally removing a tag
General questions about tag usage on the main site
Questions that deal with our cleaning up unwanted junk tags.
231 questions
Use this to tag anything about asking questions in general
215 questions
Anything about questions that were closed by community or a moderator
182 questions
If you have any issues with a specific question, use this tag. Include the link to the original question, if possible.
Questions regarding reputation, see also [voting] and [privileges]
144 questions
Anything related to posting answers, e.g. about improving their content, voting on answers, editing others' answers, etc.
138 questions
Anything related to the editing feature, e.g. anonymous edits, suggested edits, the editing privilege, edit history, etc.
To ask about flags, how to flag, when to flag, how flags work, and explanation why flags are declined.
126 questions
Requests to have closed questions reopened by community or a moderator. Please include arguments – why should the question be reopened?
124 questions
124 questions
A request to add one tag as the synonym of another tag. Please be specific about which tag should be a synonym of which. Bidirectional synonyms and cycles are implicitly disallowed, so suggest wisely.
124 questions
Comments that can be added to questions or answers
Questions about the migration of posts to another Stack Exchange site
103 questions
For questions about the /review path where users can view and act on posts by other users that the system thinks may need attention.
102 questions
Relating to the Super User Blog, including questions, topics, reviews, and requested features.
90 questions
Questions about finding duplicates, handling duplicate content, voting to close, et cetera
89 questions
Questions about reasons for closing a specific question (use [specific-question] too), and the predefined reasons users are able to choose from when voting to close
82 questions
Questions about current moderation policy and support about the way moderation works
70 questions
in scope in superuser.
69 questions
for questions specific to down-votes, the community's way of telling peers that their content can be improved. Down-votes on meta site have different meanings.
65 questions
Any concerns about the scope of the site, as explained in the FAQ
55 questions
54 questions
2 3 4 5