A hidden file is a file that exist on a computer, but don't appear when listing or exploring the files. A hidden file is primarily used to help prevent an important file from being accidentally deleted. However, hidden files should not be used to hide any confidential information since any user can view any hidden file.
In Microsoft Windows Explorer, a hidden file will appear as a ghost or faint icon. For example, 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 the files. Files may also have file permission rights that allow or prevent users from viewing the files. In order to view these files, you must be given the appropriate rights by the administrator or super user.