Localhost is an address/term used for testing connection to the local host (current computer) used for some network troubleshooting
localhost (all lowercase) (meaning this computer in computer networking) and is the standard hostname given to the loopback network interface.
IPv4
Under IPv4 the standard localhost address is normally assigned to:
127.0.0.1
IPv6
In full notation, the address under IPv6 is:
0:0:0:0:0:0:0:1