The noun ecology describes the environment as it connects to living things, or the branch of biology that studies that environment.
The German zoologist Ernst Haeckel coined the word ecology almost 150 years ago, and it should come as no surprise — his being a serious scientist and all — that he combined a couple of Greek words to do it. Oikos means "habitation" and -ology means "the study of." So ecology started off as the study of where things live. More and more, though, the word is used interchangeably with environment.