127.0.0.1 is the standard IPv4 loopback address for referring to the local computer itself.
Traffic sent to this address does not travel through the physical network to another machine. Instead, the operating system loops it back internally. Developers use it to test web servers, databases, and other network software on the same computer.
The entire IPv4 block from 127.0.0.0 through 127.255.255.255 is reserved for loopback traffic, although 127.0.0.1 is by far the best-known address. The hostname `localhost` commonly resolves to it, though local configuration can also associate localhost with other loopback addresses.
It is not the same as a private router address such as 192.168.1.1. A private address identifies a device on a local network, while 127.0.0.1 identifies the current device internally.