PRN (printer port)・LPTn (parallel port) - DOS/Command Prompt Reference
‘LPTn’ is a kind of device file name, referring to parallel ports. n is a number such as 1, 2, etc. and LPTn would be ‘LPT1’, ‘LPT2’, ..., and ‘LPT9’.
‘PRN’ also refers to serial port, and is treated as same as ‘LPT1’.
print /D:LPT2 doc.txt
Specifies the output target to ‘LPT2’ for Print command.
echo cmdtext > PRN
Sends the text ‘cmdtext’ as a command to PRN. (The target device must recognize this command.)