Normally, index.html or index.php are the files that are retrieved when a client requests a directory. For example, when a user types http://www.kuzzuk.net/weblog the browser looks for and retrieves files like index.html, index.php or default.html but lets say I want to show a Flash page first (dreadful idea to have Flash page) then I’d add this line on my .htaccess file within the weblog folder.

DirectoryIndex flash.php index.php

This means that the browser will first retrieve flash.php before the default index.php.