On-Premises environments are available in different configurations suited for different roles and applications.
Concurrent Users
The listed number of concurrent users determines the maximum number of end users who can interact with your application at the same time.
Even if an On-Premises configuration does not set a limit on the number of concurrent users, you may find that there is a practical limit that your application can support, as discussed here.
Configurations that limit the number of end users are not recommended for production applications, but are suitable for development, QA, and pre-production roles.
Server CPUs
Defines the number of CPUS (as seen by Java) that the On-Premises environment will make use of, regardless of the number of CPUs that are on the Server. Unlimited Server CPU configurations will use as many CPUs as it requires up to the number available on the Server.
Configurations that limit the number of CPUs used are not recommended for production applications, but are suitable for development, QA, and pre-production roles.