Whats Referrals and Group Memberships

ex.

Referals - when you join, you can type in a username who told you about the forum, but seeing as this forum has a custom sign-up page you can't

Group Membership - Global Mod, Mod, Admin etc

Thanks for clearing that up. I always thought group membership had something to do with leagues are teams maybe. The referals were a complete mystery to me, but I never cared enough about it to ask.