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 sandbox questions, which allow people to write answers meant for testing of a particular issue, or a draft for a later answer.
an open standard that allows users to log in to many websites with a single set of third-party credentials.
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…
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…
for questions regarding unregistered users.
For questions involving the "Ignored Tags" specified in a user's Preferences. Questions with these tags are dimmed or removed entirely from question lists.
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.