NoMachine server products take into consideration the number of connections and, in the case of the Terminal Server family for Linux, also the number of concurrent virtual desktops.
The connections limit counter counts all types of connections. These can be connections to the physical desktop, to virtual desktops, custom sessions, sessions which have been reconnected, and also sessions connected to other users' virtual desktops.
The virtual desktops limit counter counts only new virtual sessions (desktop or custom), and as mentioned above, virtual desktops are only available in the Terminal Server for Linux products: Workstation, Small Business Server, Terminal Server and Enterprise Terminal Server.
When a user connects, the connections limit counter is always increased, while the virtual desktops limit counter is increased only when the user creates a new virtual desktop or a new custom session.
When a user disconnects, the connections-limit counter is decreased. The virtual desktops limit counter is decreased only when the user explicitly terminates the virtual desktop or custom session running on the Linux Terminal Server host.
Limits on concurrent virtual desktops and concurrent connections explained