If a server has the following in /etc/sudoers: Defaults targetpwALL ALL=(ALL) ALLThen what does this mean? all the users can sudo to all the commands, only their password is needed? 
What does ALL ALL=(ALL) ALL mean in sudoers?
sudo
From the sudoers(5) man page:The sudoers policy plugin determines a user's sudo privileges.For the targetpw:sudo will prompt for the password of the user specified by the -u option (defaults to root) instead of the password of the invoking user when running a command or editing a file.sudo(8) allows you to execute commands as someone elseSo, basically it says that any user can run any command on any host as any user and yes, the user just has to authenticate, but with the password of the other user, in order to run anything.The first ALL is the users allowedThe second one is the hostsThe third one is the user as you are running the commandThe last one is the commands allowed