1. The study of living organisms, divided into many specialized fields. (wikipedia.com)
2. The plants and animals of a particular area. (wikipedia.com)
3. The science of life and of living organisms, including their structure, function, growth, origin, evolution, and distribution. It includes botany and zoology and all their subdivisions (Aquarena Wetlands Project Glossary of Terms, http://www.bio.txstate.edu/~wetlands/Glossary/glossary.html)
4. The characteristic life processes and phenomena of organisms, e.g. the biology of viruses (biology-online.org)
Word origin: from the Greek word βίος, bios (life) and the suffix -λογία, –logia (study of).