MediaWiki Administrator's Handbook/Protect
Protect prevents changes to a page by users below a certain user level.
- Default: anyone can edit
- Autoconfirmed: No IP editing, no editing by the newest accounts
- Sysop: only editable by administrators
Pagemove permissions are "locked" by default to match the edit permissions, but can be unlocked to allow editing without allowing pagemoves, or in theory vice-versa (though there's rarely any reason to set it that way). This is often done to project namespace pages which should be editable by anyone, but should not be moved around.
Protecting the main page does not automatically protect the talk page.
What should be protected depends on the project, but generally:
- Project and help namespace pages should generally be protected against pagemoves.
- Policy pages may be protected
- Widely used templates
- Frequent vandal or spam targets (the different projects have vastly different rules governing when this should be done)
- User namespace pages, on request of the user.
- For a more general discussion, see Protected pages considered harmful (on meta).
Local Policies 
- en.wikipedia -- Wikipedia:Protection policy
- en.wikibooks -- Wikibooks:Semi-protection policy
- en.wikiversity -- Wikiversity:Page protection templates
- commons.wikimedia -- Commons:Protected page
- en.wiktionary -- Wiktionary:Protected page guidelines
- en.wikisource -- Wikisource:Protection policy
- en.wikiquote -- Wikiquote:Protected page
- en.wikinews -- Wikinews:Protection policy