Zoology (, zoh-OL-luh-jee) or animal biology is the branch of biology that relates to the animal kingdom, including the structure, embryology, evolution, classification, habits, and distribution of all animals, both living and extinct, and how they interact with their ecosystems. The term is derived from Ancient Greek ζῷον, zōon, i.e. "animal" and λόγος, logos, i.e. "knowledge, study".