A person who believes in the power and structure of authority. Socially they believe in a solid to extreme structure of rules. Also they tend to believe in heavy regulation of businesses and corporations.
Authoritarians tends to become a bad label due to some heavy state heavy dictators that can form from an extreme level of these beliefs. I repeat ... authoritarian and dictator are not synonyms (contrary to the beliefs of libertarians, and other exaggerating morons)
These people believe that in order to maintain safety and well being of everyone, that the social liberties of the individual be regulated. This would mean heavy government influence in business and society. In essence State > Individual and that the Whole is greater than or equal to its parts.
They tend to believe in harsher more than a wrist slap punishment to deter further misconduct. They believe that rules are there for a decent reason and should not be disobeyed.
This is contrary to Libertarian, who tends to believe in as little government regulation especially when it comes to social regulation (they are a little more okay with it in businesses). In summary Individual > State and that the Parts are greater than or equal to the whole.
(student texting in class after getting caught): Hey don't take away my phone! Free speech dude!! I have the right to my cell phone at all times!
(Teacher) Cell Phones are for emergencies, it is disrespectful to text in class, you should be paying attention even if what I am teaching is boring
(Libertarian) We are responsible members of society, and we do not need rules or regulations to make us act responsibly! *I* HAVE RIGHTS !
(Authoritarian) You are not ALL responsible and unfortunately you must be protected from yourselves, come down from your fantasy land and take a little bit of reality in, *EVERYONE* will be better off this way.