An environment is made up of the circumstances, objects, or conditions by which a human, animal, plant or object is surrounded. In science, the word milieu is also used to denote environment to avoid confusion with the science of ecology or human social reality.
In politics, the term the environment generally refers to the natural world as perceived by humans, with particular reference to damage done by mankind, or impact of this damage on human beings. Efforts to reduce this impact--such as reducing pollution, advocating lower consumption of petroleum, and switching to renewable energy--are usually collectively called environmentalism.
This is in contrast to the term "ecology" which refers to the operations and cycles of life in the natural world, without reference to mankind except as observer. When used politically it refers more to preservation of natural capital for sustainable use, and the right of other species to exist for their own sake and not suffer extinction, as opposed to being part of a human environment.