It is called Routing. You need to do it in /application/routes.php file. Htaccess file should be:
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php/$1 [L]
And in routes.php add following line:
$route['events'] = "prefiltered";
Hope it helps.