Roles
The roles people in the account are given, which decide what they may see and do.
A role is a set of permissions that people in the account share, such as "Web editors". Give a role a permission and everyone in it has that permission. Roles used to be called groups, and some fields still use that name.
Every account starts with two roles: Everyone, which every user is in, and Account administrators. A role is also an assignee, so it can be given things the way a person can.
In Silktide itself: Roles screen, in Help.