CodeIgniter comes with an "Auto-load" feature that permits libraries, helpers, and models to be initialized automatically every time the system runs. If you need certain resources globally throughout your application you should consider auto-loading them for convenience.
To autoload resources, open the application/config/autoload.php file and add the item you want loaded to the autoload array. You'll find instructions in that file corresponding to each type of item.
See the original documentation page.