loopback
also: lo, localhost, 127.0.0.1, loopback interface
A virtual network interface that allows a computer to communicate with itself, typically assigned the IP address 127.0.0.1 on IPv4. It's used for testing network software without requiring physical network hardware.
The loopback interface is a special virtual network device that routes data back to the same machine instead of sending it out over a physical network. On most Linux systems, it's named lo and is automatically configured with the IP address 127.0.0.1 (IPv4) and ::1 (IPv6).
Loopback is essential for local inter-process communication and testing. For example, a web developer can run a web server on 127.0.0.1:8080 and test it by visiting http://localhost:8080 in a browser without needing network connectivity.
You can view the loopback interface with ip addr show lo or ifconfig lo. Any traffic sent to a loopback address is processed by the kernel's network stack and returned to the sender, making it ideal for debugging and running services locally.