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.
identifies questions about the site's topic. This tag must not be used to identify questions about constructiveness or not a real question scenarios unless the question also includes doubts a…
used to identify questions that are directly related to moderation, whether it be moderation by the community or diamond moderation.
used to identify questions that involve using editing as a community tool to improve the quality of both questions as well as answers.
to indicate you've found an erroneous or unexpected behaviour that needs to be fixed on this site (Project Management - Stack Exchange).