Ecosystem: a biotic community and its surroundings, part inorganic (abiotic) and part organic (biotic), the latter including producers, consumers, and decomposers. The term was introduced in 1935 by Sir Arthur Tansley. Social ecologist Murray Bookchin prefers the less mechanical word ecocommunity. Its components are not reducible to the interdependent relationships that emerge from it. (From: A Glossary of Ecological Terms)
The term ecosystem (or ecological system) refers to communities of organisms and their environment. Ecosystems can vary greatly in size. Small ecosystems occur in tidal pools, in a back yard compost pile, or in the rumen of an individual cow. Larger ecosystems can include a lake or forest. Landscape-scale ecosystems comprise still-larger regions. Ultimately, all of Earth's life and its physical environment represents an ecosystem known as the biosphere.