Server : A server is a computer in network that provides services to the client computers such as logon requests processing, files access and storage, internet access, printing access and many other types of services. Servers are mostly equipped with extra hardware such as plenty of external memory (RAM), more data store capacity (hard disks), high processing speed and other features.
Network Server is a computer in Network that is designated to provide one or more network service. For example file server, database server etc.
A network server designated to provide one particular service is known as dedicated server. For example if a computer is assigned for database service only then that computer is known as dedicated database server.