peat, Organic fuel consisting of a light, spongy material formed in temperate, humid environments by the accumulation and partial decomposition of vegetable remains under conditions of poor drainage. Peat deposition is the first step in the formation of coal. Dried peat burns readily, with a smoky flame and a characteristic odour. It is used for domestic heating and can be used to fire boilers. It is only a minor contributor to the world energy supply, but large deposits occur in Canada, China, Indonesia, Russia, Scandinavia, and the U.S. Major users include Finland, Ireland, Russia, and Sweden.