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It shows up as a "USB serial" device, a USB standard for emulating RS232 serial ports. Not to be confused with the S in USB :)

You can use a terminal program, or eg GNU Screen, on the /dev/tty?? device on Unixy systems (COM ports on Windows).

As a software developer that, at one point in a job, was forced to confront hardware head on because the code I was writing was firmware, I'm guessing they mean something like Kermit. A simple tool to get the output from an embedded device.

It's just exposes a UART (serial port) to USB device. With the right driver you'll get a serial port (ttyUSB, COM port, etc.) in your OS/

The USB acts as a serial interface that spits out a lot of text for you to consume. They probably have a dedicated core for debugging on the silicon.