Loopback is a networking term that refers to a communication channel that sends data back to the same device. It is commonly used for testing and troubleshooting network applications. The most well-known loopback address is 127.0.0.1, which allows a computer to communicate with itself. In programming, loopback can also refer to a method where a system sends data to itself for processing. This technique is useful for debugging and ensuring that data is handled correctly before being sent to other systems. Overall, loopback serves as a valuable tool in both networking and software development.