The term authoritarian is defined as the enforcing or favoring strict obedience to authority with the personal freedom being at expanse.
This term can be used for people that do have high authority, be it in the politics, economy, military...
Usually, something that is ruled by a person that is authoritarian ends up badly for everyone, as most of the people that are bellow that person in the hierarchy suffer, and eventually they get sick of it and take down that person.
Usually the term is used for leaders of countries in more recent times, where we have leaders that have absolute power in their countries, everyone has to obey them, and they rule with iron fist. Some examples of the near past are Hitler, Stalin, Mao Zedong, Pol Pot, Tito, Castro, while from the present day its Kim Jong Un, Berdimuhamedow, Myint...
The authoritarians come in the form of dictator, tyrant, despot, absolutist, autocrat.