localhost is the default name assigned to the loopback address of a computer.
A loopback is a communications channel with only a single destination; any message transmitted through such a channel is immediately returned to the transmitting device. A loopback interface is not physically connected to a network; rather, it is an entirely software function that emulates many of the functions of a real network interface.
A loopback address is an IP address that is designated for loopback use. By default it is 127.0.0.1 in the currently mainstream IPv4 Internet protocol addressing scheme, and it is ::1 in its successor, IPv6.
Having a loopback address for a computer allows the user to communicate with it as though it were a remote machine (i.e., a computer located elsewhere on the network). This is useful for testing of network-oriented services and programs, and it is also used by some programs during normal operations.
Created October 10, 2005.