Noun
1. Branch of biology that deals with the study of the preservation, protection, or restoration of the natural environment, natural ecosystems, vegetation, and wildlife (dictionary.com)
2. The branch of biology that deals with the effects of humans on the environment and with the conservation of biological diversity. (The American Heritage® Dictionary of the English Language, Fourth Edition copyright ©2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company)
3. The scientific study of the nature and status of Earth’s biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction and the erosion of biotic interactions. It is an interdisciplinary subject drawing on sciences, economics, and the practice of natural resource management. (Wikipedia.com)