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.
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.
For questions about changing site name from Programmers.
These questions are the most frequently asked and answered questions on Meta.
use for any questions related to deleted answers specifically.
Cleanup Initiative, a program to systematically destroy bad, honeypot tags.
The user profile page, which contains a list of all the questions, answers, and an audit trail of the user's activity on the site
questions asking for resources - books, links, tutorials, articles, tools, libraries etc