I gave this answer to a duplicate, and thought I'd post it here for your reference:
As previously stated. It's a reserved word from back in MS-DOS, for the CONsole device (as far as I can remember). But, you can force Windows/dos to create the folder for you. For devices, it uses the format
\\.\[RESERVED_WORD] to access the "file" (these devices used files for communication). To force Windows to create your folder, instead of doing
mkdir [RESERVED_WORD], do the following:
mkdir \\.\[absolute path to folder of choice, including drive letter]\[RESERVED_WORD]
For example, to create CON folder on my desktop,
To delete the folder, you have to reference it the same way, or else it won't work.
My advice though is to just use a different name. It would be very difficult to always refer to it via its absolute path, especially if you are developing an app you plan on deploying.