Democide refers to "the intentional killing of an unarmed or disarmed person by government agents acting in their authoritative capacity and pursuant to government policy or high command". The term, first coined by Holocaust historian and statistics expert R. J. Rummel in his book Death by Government, has been described by renowned Holocaust historian Yehuda Bauer as a better term than genocide to refer to certain types of mass killing. According to Rummel, this definition covers a wide range of deaths, including forced labor and concentration camp victims, extrajudicial summary killings, and mass deaths due to governmental acts of criminal omission and neglect, such as in deliberate famines like the Holodomor, as well as killings by de facto governments, for example, killings during a civil war. This definition covers any murder of any number of persons by any government.

Rummel created democide as an extended term to include forms of government murder not covered by genocide. According to Rummel, democide surpassed war as the leading cause of non-natural death in the 20th century.

Democide is the murder of any person or people by "their" government (normally the one under whose jurisdiction they live), including genocide, politicide, and mass murder. Democide is not necessarily the elimination of entire cultural groups but rather groups within the country that the government feels need to be eradicated for political reasons and due to claimed future threats.

According to Rummel, genocide has three different meanings. The ordinary meaning is murder by government of people due to their national, ethnic, racial or religious group membership. The legal meaning of genocide refers to the international treaty on genocide, the Convention on the Prevention and Punishment of the Crime of Genocide. This also includes nonlethal acts that in the end eliminate or greatly hinder the group. Looking back on history, one can see the different variations of democides that have occurred, but it still consists of acts of killing or mass murder. The generalized meaning of genocide is similar to the ordinary meaning but also includes government killings of political opponents or otherwise intentional murder. In order to avoid confusion over which meaning is intended, Rummel created democide for this third meaning.

In "How Many Did Communist Regimes Murder?", Rummel wrote:

First, however, I should clarify the term democide. It means for governments what murder means for an individual under municipal law. It is the premeditated killing of a person in cold blood, or causing the death of a person through reckless and wanton disregard for their life. Thus, a government incarcerating people in a prison under such deadly conditions that they die in a few years is murder by the state—democide—as would parents letting a child die from malnutrition and exposure be murder. So would government forced labor that kills a person within months or a couple of years be murder. So would government created famines that then are ignored or knowingly aggravated by government action be murder of those who starve to death. And obviously, extrajudicial executions, death by torture, government massacres, and all genocidal killing be murder. However, judicial executions for crimes that internationally would be considered capital offenses, such as for murder or treason (as long as it is clear that these are not fabricated for the purpose of executing the accused, as in communist show trials), are not democide. Nor is democide the killing of enemy soldiers in combat or of armed rebels, nor of noncombatants as a result of military action against military targets.

In his work and research, Rummel distinguished between colonial, democratic, and authoritarian and totalitarian regimes. He defined totalitarianism as follows:

There is much confusion about what is meant by totalitarian in the literature, including the denial that such systems even exist. I define a totalitarian state as one with a system of government that is unlimited constitutionally or by countervailing powers in society (such as by a church, rural gentry, labor unions, or regional powers); is not held responsible to the public by periodic secret and competitive elections; and employs its unlimited power to control all aspects of society, including the family, religion, education, business, private property, and social relationships. Under Stalin, the Soviet Union was thus totalitarian, as was Mao's China, Pol Pot's Cambodia, Hitler's Germany, and U Ne Win's Burma. Totalitarianism is then a political ideology for which a totalitarian government is the agency for realizing its ends. Thus, totalitarianism characterizes such ideologies as state socialism (as in Burma), Marxism-Leninism as in former East Germany, and Nazism. Even revolutionary Moslem Iran since the overthrow of the Shah in 1978–79 has been totalitarian—here totalitarianism was married to Moslem fundamentalism. In short, totalitarianism is the ideology of absolute power. State socialism, communism, Nazism, fascism, and Moslem fundamentalism have been some of its recent raiments. Totalitarian governments have been its agency. The state, with its international legal sovereignty and independence, has been its base. As will be pointed out, mortacracy is the result.