In ZenGRM Enterprise, the architecture is based around a top-level 'Admin Unit', having administrative control over any number of 2nd-tier, linked 'Business Units' and Users in the organization.
Your Admin Unit will have been assigned a maximum number of Business Units and Users, depending on your organization's subscription level.
You can think of your Admin Unit as your 'corporate account' and each Business Unit as a different department, location, sales office or working group within your corporation; basically any sub-group of people who may need to create and manage their own events and contacts.
Each Business Unit is created at this top-level Admin Unit. Each Business Unit added via the Admin Unit top-level is counted against the Business Unit Limit in your organization's subscription.
All Users added at the Admin Unit top-level can then be assigned access to any one or more of your Business Units. Each individual User added at the Admin Unit top-level is counted against the User Limit in your organization's subscription.
When Users are assigned to Business Units at the Admin Unit level they are also assigned access levels within those Business Units. For example, a User can be added at the Admin Unit level - and be assigned Admin Access to Business Unit 1, and Team Member Access to Business Unit 2.
Any User with Admin Access to a Business Unit can also assign access to that Business Unit to any other existing system-side User - but can only assign them the roles of either Team Member or Viewer (i.e. Business Unit Admin Users cannot assign existing users as additional Admin Users to their Business Unit. Only Admin Unit admins can do that)