Manual:$wgAllowPageInfo

Details
This setting, if enabled, allows users to get some extra information about the page by specifying "action=info" in the URL.

For example, entering  might generate the following (fictional) output instead of the main page contents:

Information for "Main Page" Information for page

Currently you have to add the action manually to the URL, as there is no link to this page regardless of the value of this setting. See bug 16362.

Note that on Wikimedia servers (e.g. Wikipedia, Wiktionary, etc.) this function is disabled, as it is very inefficient and because it allows potential vandals an easy way to find unwatched targets.