A dotfile is any file (or directory) prefixed by a period ('.'). On UNIX systems, dotfiles are hidden from the output of ls. To see the files, use "ls -a". They are not truly hidden, but by convention programs that deal with the user should not show any filename starting with a dot unless the user says otherwise. The uses of dot-files vary, but they should not be considered truly hidden, or secure, despite the name of "hidden files". However, because of the convention they can be used by crackers to hide their root kits from unsuspecting users or system administrators.
This means that they are not included in the file list you get with an asterisk in the shell:
tweedleburg:~ # mkdir test tweedleburg:~ # cd test tweedleburg:~/test # touch .testfile tweedleburg:~/test # touch file1 tweedleburg:~/test # ls -a .testfile file1 tweedleburg:~/test # ls * file1 tweedleburg:~/test #
As you see in the example above, the files .testfile and file1 exist, but only file1 is shown for ls *.
Dotfiles can be used to reduce clutter in a user's home directory,
tar cvzf backup.tar.gz *
will NOT save your dot files, better use
tar cvzf backup.tar.gz .