Help:Page validation

Page validation is a quality control mechanism implemented by the FlaggedRevs extension which allows users with the proper access level to review modifications made by others and sign off on their impression of the quality of those edits.

With page validation in place, multiple revisions of an article are live at one time:
 * The published version of a page, which has met with a reviewer's explicit approval, appears to all visitors of the site, including those who are not logged in or do not have a user account.
 * The draft version of a page is the version which contains all unreviewed edits. This version of the page is visible by default to logged-in registered users, and is visible to anonymous visitors only if they click on the revision icon in the upper right hand corner of the article. This icon, which represents and describes the review status of the article, offers the ability to change the version of the page that is being viewed.

The actual checking is done by users with the Editor permission; see Help:User groups.