Users with the Oversight class will have an additional 'hide revision' tab when viewing an old revision, edit difference, or deleted revision. The edit can be hidden from all users by clicking this tab, adding a reason, and confirming. The most recent edit to a page cannot be hidden unless the page is deleted; to hide it, you must first revert or delete the edit.
Note that hiding revisions may create misleading edit differences, since any changes made in hidden revisions will seem to have been made by the next visible edit. In situations where good content is added in hidden revisions, there may be no simple solution. The extension may eventually replace the removed revisions with an explicitly visible marker instead. (It should be noted that the core RevisionDelete does leave a marker.)
The "Oversite" extension has been replaced by core functionality in the MediaWiki software (which was added in version 1.16.0). For details see: MediaWiki Extension:Oversite