The Administrator is not limited by any user rights restrictions and can perform all functions in Memsource.
Every organization account in Memsource must have at least one Administrator user.
In terms of licensing, Project Managers and Administrators are interchangeable; if there are three PM licenses, at least one must be an Administrator.
As a role, the administrator is typically responsible for:
Any change of payments for the Memsource account (as well as any edition changes or upgrades).
White-labeling the system (e.g add a custom logo).
Creating/editing/deleting projects, jobs, translation memories, and term bases.
Creating/editing/deleting other users.
Organization settings under Setup.