Decimation originally denoted a cruel and barbaric form of disciplining a unit of military field personnel for failure, or at worse an arbitrarily inflicted measure by a ruthless commander for trivial infractions of military discipline, to maintain terror and obedience among his command. One of every ten (Latin decem) soldiers or sailors is chosen by lot at random to be executed by their fellows as a punishment for their collective failure to fulfill orders, or as an arbitrary means of enforcing discipline in the ranks by fear of the commander or staff of commanders under a chief commander. It was also inflicted on captives of war and villages and cities as a means of terror or reprisal.
The MGM film Paths of Glory, 1957, directed by Stanley Kubrick and starring Kirk Douglas is a story of French military decimation in World War I, based on the infamous Souain corporals affair, in which four French soldiers of the 10e Compagnie of 8 Battalion of the Régiment Mixte de Tirailleurs Algériens were executed for mutiny. During the retreat at the beginning of the war these French-African soldiers refused an order to attack. They were shot on 15 December 1914 near Zillebeeke in Flanders. Their families sued, and while the executions were ruled unfair, two of the families received one franc each, while the other two received nothing.
More generally, to decimate is to destroy or kill a large proportion of a (human or animal) population, also land or property.