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.
a flag that can be applied to answers (and questions) which lowers the barrier for editing and prevents any rep gain/loss from voting.
Briefly, a hackathon brings people together to use technology to transform ideas into reality.
a reference to data or content that the reader can directly follow either by clicking, hovering over, or that is followed automatically. (Ref. Wikipedia)