Role

A role is something a server administrator can give to a user, or, depending on the role's permissions, a user can assign one to themselves.

A server's roles can be managed in the settings, which can be accessed by clicking the arrow in the upper left hand corner when in a server (and if you have the appropriate permissions)

Role name
When you've created a role, you can give that role any name of your choice.

Role color
The role color can be changed, which will change the color of any user's name all throughout the server.