A dotfile is a file whose names begin with a .. These are normally hidden by ls and not listed unless requested.
For example the following output of ls:
$ ls
bin pki
The -a or --all option will list all files, including dotfiles.
$ ls -a
. .ansible .bash_logout .bashrc .lesshst .puppetlabs .viminfo
.. .bash_history .bash_profile bin pki .ssh
The -A or --almost-all option will list all files, including dotfiles, but does not list implied . and ... Note that . is the current directory and .. is the parent directory.
$ ls -A
.ansible .bash_logout .bashrc .lesshst .puppetlabs .viminfo
.bash_history .bash_profile bin pki .ssh