Closing a question effectively means that it can't be added to or answered. The question can however still be edited and commented on. This normally happens if it is a duplicate question, or various other reasons depending on the site.
The voting process works differently depending on your level.
- 250+ allows you to vote to close your own questions. The change still requires 4 more votes.
- 3000+ rep users can vote to close, and 5 votes are needed until the question is closed.
- Diamond moderators can close immediatly.
These question remain in the system, and can either be voted to be re-open or deleted. The same voting rules apply for these options.
Only deleted questions are removed from the system after 3 days if memory serves.