AUX (including AUX.*, in any directory on Windows ) is a special “file” representing a hardware device (by default, tue first serial port, same as COM1); trying to copy to or from a file name matching that pattern results in accessing the device instead.

There are a bunch of these special files. [0]

[0] A list is deep on this page: https://docs.microsoft.com/en-us/windows/win32/fileio/naming...