localhost is the name of the computer itself, and the term loopback network interface refers to the virtual interface that connects to itself. 127.0.0.1 is the default IP address for this loopback interface. Other IP address are also available pointing to this host, actually it’s the whole subnet of 127.x.x.x.
Programs on the same computer could communicate with each other using 127.0.0.1, also, we could ping 127.0.0.1 to verify that the protocol stack on the computer is working correctly.
The packets send to 127.0.0.1 is not allowed to be put on to the actual network. So it could bypass the network hardware to test the network software.
There are also other special addresses such as 192.168.1.1, which is mainly used for home routers.
