Files that exists on a computer, but don't appear when listing or exploring, are called hidden files. A hidden file is primarily used to help prevent important data from being accidentally deleted.
Tip: Hidden files should not be used to hide confidential information as any user may view them.
In Microsoft Windows Explorer, a hidden file appears as a ghost or faint icon. In the picture below, there are three files with a "hidden.txt" hidden file. As can be seen, the icon is much lighter than the other two icons.
In MS-DOS or the Windows command line, when the dir command is used without any additional switches, you cannot see hidden files. However, using the "attrib" or "dir /ah" command enables you to view any hidden files in the current directory.
Note: It is important to realize that files can also be hidden using a software program or other commands. In order to view these files, you need access to the program used to lock them. Files may also have permission rights that allow or prevent users from viewing, which may only be given by the administrator or superuser.