In operating systems, the term terminal host traditionally denotes a multi-user computer or software providing services to computer terminals, or a computer that provides services to smaller or less capable devices, such as a mainframe computer serving teletype terminals or video terminals. Other examples are a telnet host (a telnet server) and an xhost (X Window client).
The term "Internet host" or just "host" is used in a number of Request for Comments (RFC) documents that define the Internet and its predecessor, the ARPANET. While the ARPANET was developed, computers connected to the network were typically mainframe computer systems that could be accessed from terminals connected via serial ports. Since these dumb terminals did not host software or perform computations themselves, they were not considered hosts. The terminals were connected to the terminal hosts through serial interfaces and perhaps circuit switched networks, but not connected to any IP based network, and were not assigned IP addresses. Today's IP hosts may, however, lack the ability to serve as terminal hosts.