A coup d'etat is a French term meaning to forcibly take over (or attempt to take over) the government of a country by the military of that country, generally carried out by violent or illegal means. It differs from a revolution in that it is usually carried out by a small group that proceeds to install its leader as head of government rather than being a mass uprising by the people.
Early examples of coups include the coup of 1799, in which Napoleon overthrew the Revolutionary Directory and declared himself first president of France. Coups in more recent times include the overthrow of the socialist government of Chile 1973, the military seizures of power in Nigeria 1983, the Great Myanmar Coup of 1988, Gambia 1994, the short-lived removal of Mikhail Gorbachev from power in the USSR by hard-line Communists in August of 1991, and the overthrow of president Ahmad Tejan Kabbah in Sierra Leone in February 1998.
The German word putsch is sometimes used to describe a coup, as in the Beer Hall Putsch of 1923.