Microsoft Dynamics GP offers three types of user licenses: Full, Limited, and Self-Serve. These are either Concurrent or Named licenses which will depend on both the type of licenses and how it is deployed.
Concurrent user licenses are limit the number of people that can be logged into the system at one time. If you had 10 concurrent full user licenses, you could set up 100 people to be able to log into the system, but only 10 could access the system at any one time.
Named User Licenses
Every person needs their own license. This means generic user names that are used for 2-3 different people are not allowed.