Peat is partially decomposed plant material, the plants usually being grasses or mosses. It requires the presence of water to prevent oxidation or bacterial destruction. It is normally dark brown in colour. Where prevalent, it establishes a particular environment for lime-intolerant plants and some forms of animal life.
Peat is inflammable when dried out and has been much used as a household fuel. It is not as dense as coal. A slab of peat used for fuel is known as "a peat". Its extraction has been a considerable industry in certain areas, with its own tools and terminology.
The peat extraction industry continues, particularly in providing peat as a basis for garden "compost". This use exploits its potential as a soil conditioner to which other ingredients may be added. As peat takes a very long time to develop, the industry has been criticised for large-scale destruction of a certain type of habitat.