What is the difference between admin and sub-admin on a forum?

On a forum what is the difference between admin and a sub admin or co admin?
and what's the difference between a moderator and a super mod?
Thanks? just confused.
i know what mods and admins are just not the others?

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia��).