Despotism is a form of government in which a single entity rules with absolute power. That entity may be an individual, as in an autocracy, or it may be a group, as in an oligarchy. The word despotism means to "rule in the fashion of a despot" and does not necessarily require a singular "despot", an individual.
Despot comes from the Greek despotes, which roughly means "master" or "one with power", and it has been used to translate a wide variety of titles and positions. It was used to describe the unlimited power and authority of the Pharaohs of Egypt, employed in the Byzantine court as a title of nobility, used by the rulers of Byzantine vassal states, and adopted as a title of the Byzantine Emperors. Thus, despot is found to have different meanings and interpretations at various times in history and can not be described by a single definition. This is similar to the other Greek titles basileus and autokrator, which, along with despot, have been used at various times to describe everything from a local chieftain to a simple ruler, king or emperor.
Colloquially, despot has been applied pejoratively to a person, particularly a head of state or government, who abuses their power and authority to oppress their people, subjects or subordinates. In this sense, it is similar to the pejorative connotations that have likewise arisen with the term tyrant. Dictator has also developed nearly similar pejorative connotations, though despot and tyrant tend to stress cruelty and even enjoyment therefrom, while dictator tends to imply more harshness or unfair implementation of law.