This option makes Drupal emit "clean" URLs (i.e. without ?q= in the URL).
You can find this under Administer and Site Configuration.
It is recommended that you turn on (enable) clean URLs, although other than making the URLs look a little prettier, contrary to popular belief, it does not effect your ranking in Google or other search engines anymore. This may have been true many years ago, but all the search engines have adapted to data driven pages, since most new websites use data driven pages now.
Save Configuration to continue.
