a very special device that allows you to mount a normal file as it was a physical device
a virtual device that your Linux system can access in the same way as any physical device
a Linux block device which appears to store data (by using another device)
A piece of hardware used for testing a serial port or parallel port. The loopback device contains a port connector and sometimes a looped cable. The connector attaches to the port on the computer and is used during testing to send a signal out through the port and immediately have it returned through the port.