From WHMCS Documentation
Admin modules allow you to create your own pages for the admin area. These can be used to do anything you want but common examples are time or management addons specific to your needs.
One example addon provided with WHMCS is an IP Manager addon where you can add all the IP addresses under your control and a description of what they are being used for. To create your own module, you can use the IP Manager as a template. The naming convention is modules/admin/your_module_name/your_module_name.php
