Natural environmentnatural world that people deem important or valuable, for any reason — economical, aesthetic, philosophical, hedonistic, sentimental, etc.. The word ecology is often used (chiefly by non-scientists) in this same sense.
It is the implicit value system that distinguishes the common sense of environment from its scientific meaning in ecology or biology. To a scientist, for example, a pipe dumping raw sewage into a river is the environment for any organisms that manage to thrive in it; whereas in the common sense that same pipe would be considered damage to the environment. The same distinction can be made between the common use of nature (above) and its use in science (a synonym of material world).
It is the common sense of environment that underlies environmentalism — a broad political, social, and philosophical movement which advocates various actions and policies that are viewed as good for "nature". Typical environmentalist goals include reducing pollution and the consumption of non-renewable fuels such as petroleum and coal, develoment of renewable energy sources, conservation and sustainable use of scarce resources such as water, land, and fish, protection of pristine habitats, saving endangered species from extinction, establishment of nature preserves, etc..