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 concerning general recommendations on using this SE site.
Questions about how to promote Russian Language SE, in order to attract more users.
Unicode is an industry standard for encoding and handling the characters from most of the world's writing systems.
Community Wiki is a flag that can be applied to answers (and questions) which lowers the barrier for editing and prevents any rep gain/loss from voting.