This option specifies whether the domain owner will have access to the Custom Commands Webmin module. With the Custom Commands module you can extend Webmin without having to program a new module. A custom command can run any command on the system with any options you specify. Variable replacement is also available so that the user running the command can provide input or option arguments to the command, and it is possible to run the command as the logged in Webmin user, or as any user on the system (including root, but be careful with that!). This is a very powerful feature of Webmin, allowing you to add new "buttons" that perform functions specific to your environment, or that some of your users may need access to.