In addition to groups, ServiceNow also lets you associate users with departments and companies.
[cmn_department] and Company
[core_company] tables are slightly different to groups in that they have a one-to-many relationship with users; a user is only ever a member of a single department and company.
Each of these tables records relevant information: a department has a cost code and a manager, and a company may be a vendor, manufacturer, a customer or a mixture of all. Both tables are hierarchical and have a parent field.