Peat

n. dried block of bog or swamp matter used for fuel

Peat is an accumulation of partially decayed vegetation matter. Peat forms in wetlands or peatlands, variously called bogs, moors, muskegs, pocosins, mires, and peat swamp forests.
See more at Wikipedia.org...

Noun
1. partially carbonized vegetable matter saturated with water; can be used as a fuel when dried
(hypernym) vegetable matter

(n.)
A substance of vegetable origin, consisting of roots and fibers, moss, etc., in various stages of decomposition, and found, as a kind of turf or bog, usually in low situations, where it is always more or less saturated with water. It is often dried and used for fuel.
  

(n.)
A small person; a pet; -- sometimes used contemptuously.
  

Peat consists of partially decomposed plant debris. It is considered an early stage in the development of coal. Peat is distinguished from lignite by the presence of free cellulose and a high moisture content (exceeding 70 percent). The heat content of air-dried peat (about 50 percent moisture) is about 9 million Btu per ton. Most U.S. peat is used as a soil conditioner. The first U.S. electric power plant fueled by peat began operating in Maine in 1990. (DOE5)