localhost

Localhost is the standard hostname that refers to the local computer. It is used to access network services running on the same machine and to facilitate inter-process communication. Traffic addressed to localhost is routed by the operating system to the loopback interface rather than to a physical network.

In IPv4, the loopback address is 127.0.0.1; in IPv6 it is ::1. The hostname localhost usually resolves to one or both of these addresses via the system name resolver. On most systems this mapping is provided by a hosts file (for example, /etc/hosts on Unix-like systems and C:\Windows\System32\drivers\etc\hosts on Windows).

RFC 6761 designates localhost as a special-use domain name with loopback semantics. Some configurations may rely more on DNS, but the localhost entry is widely present and expected.

Typical uses include testing web servers, databases, and other services without exposing them to the network. A service bound to 127.0.0.1 or ::1 is reachable only from the local machine; binding to 0.0.0.0 or :: would expose it to other hosts as well.

Because traffic to localhost never leaves the host, it is generally safe for development and testing. However, it does not provide access to remote machines, and misconfigurations can cause local resolution to fail in certain environments.