Any operating system (OS) is software that creates a computing environment which
is higher level (more abstract) than the computer itself. A client OS uses only
resources on a local machine, while a network operating system uses at least some
remote resources in creating a consistent illusion for its users and their programs.
A network operating system is software designed to control, monitor and manage a network (eg BSD), whereas a client operating system is software designed to control computer hardware and peripherals directly attached to a computer (eg Windows). Apple products are not NOSes, but they do incorporate aspects of them.
Network Operating system or NOS is an OS that allows a system to connect to a network.In the old days of DOS networking was not a function of the Client OS, you have to also load the NOS to get connected. Now that most Client OS's imbed network connectivity the term is now seldom used.
Network operating system is an operating system that controls processes on the entire network (made up of individual clients joined together), whereas a client operating system controls processes on the individual client (end user).
A network (server) operating system is designed to provide services (file, print, networking) to client operating systems. Apple do produce an network operating system known as OS X Server.
Network Operating system allows a system to connect to a network. In the old days of DOS networking was not a function of the Client OS, you have to also load NOS to get connected. Now that most Client OS's imbed network connectivity the term is now seldom used.