Also see Terminal Server product, Microsoft software that serves the Windows desktop and applications to terminals.
Generally in information technology, a terminal server is a hardware device or server that provides terminals (PCs, printers, and other devices) with a common connection point to a local or wide area network. The terminals connect to the terminal server from their RS-232C or RS-423 serial port. The other side of the terminal server connects through network interface cards (NIC) to a local area network (LAN) (usually an Ethernet or token ring LAN) through modems to the dial-in/out wide area network, or to an X.25 network or a 3270 gateway. (Different makes of terminal server offer different kinds of interconnection. Some can be ordered in different configurations based on customer need.) The use of a terminal server means that each terminal doesn't need its own network interface card or modem. The connection resources inside the terminal server are usually shared dynamically by all attached terminals.
Some terminal servers can be shared by up to 128 terminals. The terminals can be PCs, terminals that emulate 3270s, printers, or other devices with the RS-232/423 interface. Terminals can use TCP/IP for a Telnet connection to a host, LAT to a Digital Equipment Corporation host, or TN3270 for a Telnet connection to an IBM host with 3270 applications. With some terminal servers, a given terminal user can have multiple host connections to different kinds of host operating systems (UNIX, IBM, DEC).
The term communication server is also sometimes used instead of terminal server.