A protected page is a page where normal users are prevented from editing and/or moving at all. Only a user with sysop (admin) permissions can edit or move a protected page. Likewise only sysop users can protect a page in the first place, or unprotect the page to lift the restriction.
There are several reasons why a particular page might be protected:
Most protected pages are protected because they have been repeatedly targeted with vandalism or moved to bad titles, or where it is believed that vandalism or page moves would have an unusually severe impact. Page protection limits collaboration on the wiki content, and should be avoided where possible.
Protecting and unprotecting pages
Protecting and unprotecting pages is very straightforward, but these operations require administrator permissions.
You can designate a page as a protected page by clicking the 'Protect page' tab in the drop-down menu near the top of the page and supplying a comment (a brief description of why you are protecting the page).
There are several reasons why a particular page might be protected. However there are also many good reasons for not protecting pages. As an administrator you must make this choice, and use your privileges appropriately.