The "animal realm" refers to the vast diversity of living organisms classified as animals. This includes a wide range of species, from tiny insects to large mammals, all of which share certain characteristics, such as being multicellular and heterotrophic, meaning they obtain energy by consuming other organisms. Animals are found in various habitats, including forests, oceans, and deserts, and they play crucial roles in ecosystems. Animals are categorized into different groups based on their traits and evolutionary history. Major classifications include mammals, birds, reptiles, amphibians, and fish. Each group has unique features, such as feathers in birds or scales in reptiles, which help them adapt to their environments. Understanding the animal realm is essential for studying biodiversity and conservation efforts.