su stands for `substitute user’ and not `super user.’ (Thanks to slacker for pointing out the mistake).
su - preserves the current environment variables so that they are available for the user who has been switched to.
su -l provides a login shell.
su [USER] if USER is not specified, root is assumed by default
su -c allows to run a command as the specified user
Err, not to be a jerk but actually it stands for Substitute User (http://www.linfo.org/su.html) (http://www.freebsd.org/cgi/man.cgi?query=su&apropos=0&sektion=0&manpath=Unix+Seventh+Edition&format=html)
I might also add that for most people (and for all Ubuntu derived systems) sudo -i is better, if sudo is installed.
Furthermore, sudo should always be preferred over su -c. This is because sudo is more powerful and easier to control (thus making it an absolute must on multiuser systems from the security viewpoint)
Thank you slacker. I have edited the post.