localhost

localhost means this computer in computer networking. On most computers localhost resolves to the IP address ::1 in IPv6 and 127.0.0.1 in IPv4. The localhost is useful for programmers to test software independent of a network connection. Using the localhost bypasses the network card in a computer.

Loopback

The loopback function of localhost can be used to run a network service without needing a physical network card. It can also be used to not let a network access the service that the computer is connected to.

IPv4 network standards reserve the address block 127.0.0.0/8 for loopback.