If you wish to have a user account on your Mac that is discrete so others using your Mac cannot see that user, then you can do so by the classic methods of changing the user ID for the account and then adjusting some hidden system settings to manage those accounts at the login window. While these approaches are the most compatible across different OS X versions and still work for the latest ones, if you have OS X Yosemite or later on your Mac, then there is an easy two-step approach for hiding user accounts.
The point of hiding user accounts in OS X is to keep an average user from accessing them or knowing they exist, so this involves preventing the account from being listed in standard places like the login window and fast user switching menu. In addition, keeping the user’s home folder from being visible is a plus.
sudo dscl . create /Users/USERNAME IsHidden 1
Next, run the following command to set a special file flag attribute on the account’s home folder that will hide it. This will not hide it from the system, but will instead keep it from being visible in the Finder:
sudo chflags hidden /Users/USERNAME
Alternatively you could move the user’s home folder and pair the new location back up with the account in the Advanced system preferences, or by running the following command in the Terminal:
sudo dscl . create /Users/USERNAME NFSHomeDirectory /PATH/TO/FOLDER
However, using the “chflags” command should be all that’s needed to keep the folder hidden from most eyes, and also keep the standard user account intact. Using just the above two commands, you can easily use the system preferences to create an account, and then make it vanish with minimal additional effort.