Several special file names are reserved by the system
and cannot be used for files or folders:
eg:-CON, AUX, COM1, COM2, COM3, COM4, LPT1, LPT2,
LPT3, PRN, NUL.etc
"CON" is a reserved name that dates back to the days
of MS-DOS and is short for "CONsole". The idea is
that any program could write to the screen or read
from the keyboard simply by opening and acting on a
file by the name of CON.
Like Con, many other reserve words are there which we
can’t create. They are
PRN - It stands for printer.
AUX - It stands for Auxiliary device.
COM0, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8,
COM9 - They stands for serial ports.
LPT1, LPT2, PRN - They stands for Parallel ports.
NUL - It stands for Bid Bucket.
Source(s):microsoft.com