Manual:Noindex

Noindex can be used to prevent indexing of a page by search engines. Sample code would be:

Or, if one wished to be more selective:

There are also  and   magic words. To make these work for a given namespace, one may need to adjust $wgExemptFromUserRobotsControl. One can test whether they function for a given page using.

Allowing indexing by the Internet Archiver
Here is some code you can put in your LocalSettings.php if you want to allow the Internet Archiver to index even pages you've applied  to: