An Administrator is an editor who has the extra ability to:
- Block and unblock other users
- Delete and undelete pages on the site
- Protect and unprotect pages
- Edit pages in the MediaWiki namespace (e.g. MediaWiki:Sidebar)
- View deleted edits of a page
- View any contributions by a user to pages which are deleted.
Administrators have basically the same rights as Content administrators, plus the ability to edit pages in the MediaWiki namespace.
Requests for administrator permissions are done via a custom form on Phabricator.