Manual:$wgExtensionCredits

Details
An array of extension types and inside that their names, versions, authors, URLs, descriptions and pointers to localized description messages. Note that the version, url, description and descriptionmsg keys can be omitted.

This credit information gets added to the wiki's Special:Version page, allowing users to see which extensions are installed, and to find more information about them.

This is not a configuration setting mentioned in LocalSettings.php. Typically, extension developers will write code that appends to the array contained in this global variable.

See Manual:Developing extensions

Usage
Extension developers can append to the array with the following code:

In version 1.12 and newer, descriptionmsg will override description. The value of descriptionmsg will be treated as the name of the message used for the description.

$type must be one of the following:
 * api — API extensions
 * antispam — antispam extensions
 * media (added in 1.11) — media handlers
 * parserhook — extensions that modify, add or replace functionality in the MediaWiki parser
 * skin — extensions that modify skins
 * specialpage — extensions that add special pages
 * variable (added in 1.6.0) — make a new variable
 * other — does something else

The description and author fields get parsed as wiki syntax. This is often used to provide links to the author's homepage in the author field.

Since (mw 1.18?), the author list can contain the special hackish '...' to denote other authors. The triple dot will make MediaWiki insert the version-poweredby-others</tt> message.

Example: