A company is an attribute in a user's profile. Every user belongs to one company only.
A company is not the same thing as a user group. However, for each company, the user management engine (UME) can automatically generate a corresponding company group.
Use companies to define sets of users and provide a form of delegated administration. Companies also allow for self-registration with an approval workflow.
When you configure companies, the UMEautomatically can create a group for each company.