The term Year Zero, applied to the takeover of Cambodia in 1975 by Pol Pot, is an analogy to the Year One of the French Revolutionary Calendar. During the French Revolution, after the abolition of the French monarchy (September 20, 1792), the National Convention instituted a new calendar and declared the beginning of the Year I. The Pol Pot takeover of Phnom Penh was rapidly followed by a series of drastic revolutionary agrarian socialism policies vastly exceeding those of the French Reign of Terror and culminating in the Cambodian Genocide.
The idea behind Year Zero is that all culture and traditions within a society must be completely destroyed or discarded and a new revolutionary culture must replace it, starting from scratch. All history of a nation or people before Year Zero is deemed largely irrelevant, as it will (as an ideal) be purged and replaced from the ground up.
In Cambodia, teachers, artists, and intellectuals were especially singled out and executed during the purges accompanying Pol Pot's Year Zero.