I think ping may be referring to the "Per User/Per Device or Per Server model" introduced in Windows 2003 as opposed to the long established "Per Seat or Per Server model".
In both models, the "Per Server mode" works in the same way. In this mode, the maximum number of users/devices that can access a particular server is specified. Additional licences will be required to access other servers in the organisation
With the "Per User/Per Device mode" in the new model, you either specify the maximum number of machines or the maximum number of users that will be connected to any of the servers in use in the organisation.
Let us assume you have a network consisting of 2 Servers:
In per Server mode:
If you purchased 20 CALs (Client Access Licences) for Server 1 and 30 CALs for Server 2, you could have an unlimited number of users able to access either server, but only a maximum of 20 and 30 concurrent users could access Servers 1 and 2 respectively.
In per User/per Device:
You would have to determine how many unique users/devices would need to access either server and then buy the appropriate number of CALs. So if you had 60 unique users/devices which needed to access either server, you would simply buy 60 CALs, which would be able to access either Server 1 or 2.