In an authoritarian political system obedience to the government is emphasized, and individual liberties are subjugated. This is more a value judgement than a political philosophy, and the term is often used informally to refer to a political system that one feels is too controlling and restrictive.
When it is used formally, authoritarianism refers to a government in which the power is held by a few entrenched rulers that limit the rights of their citizens, often arbitrarily. Bribery, bureaucracy, political prisoners, and generalized corruption may be common. The political system will be set up to propagate the current rulers or ruling class, and to prevent challengers from coming into power, and is often a unitary state.
Authoritarianism may be distinguished from totalitarianism because a totalitarian government will have a set of ideals greater than protecting the current ruling class, low corruption in the lower levels of the government, strong ideology beyond simply protecting the current power structure, and often a charismatic leader... although definitions vary among writers.
Countries that have authoritarian bents include Armenia, North Korea, Chad, Iran, Burma, Zimbabwe, and, many would say, the Government of the People's Republic of China. Some would hold that the USA is also trending in a distressingly authoritarian direction, although this is currently a minority opinion.