The environment can be said to comprise of all living and non-living things that occur on Earth.
It is also used in more specific formulations, describing localized phenomena.
For instance, the environment in which a child grows up usually refers to the personalities and parenting skills of his mother and father, the economic conditions in which he was raised, and the nature of his schooling.
The environment is sometimes used as a catch phrase denoting an environmentalist perspective, as in "that is bad (or good) for the environment". While this is closer to the generalized sense above, it usually refers to some specific ecological situation, for example, "acid rain is bad for the environment because it kills lakes and trees", or, "composting is good for the environment because it reduces our landfill load and returns nutrients to the soil".