Apr 24, 2017 - 09:23 AM
Closed questions are considered questions that have been adequately answered. Administrators can close questions manually within the administration area when they're looking at the Question thread and view the question setting on the right column.
See setting here:
The system will automatically close questions based on user activity as well, as an answer is recognized as being quality either through voting or its longevity. The questions are automatically closed based on if they have a best answer selected by the asking user (by giving a thumbs up vote), and/or have at least one answer posted, and is at least 3 weeks old.