The "Five Kingdoms" is a classification system used in biology to categorize all living organisms into five distinct groups: Monera, Protista, Fungi, Plantae, and Animalia. This system helps scientists understand the diversity of life and the relationships between different organisms. Each kingdom has unique characteristics, such as cellular structure and modes of nutrition. The Monera kingdom includes single-celled organisms like bacteria, while Protista consists of simple eukaryotic organisms, such as algae and protozoa. Fungi are primarily decomposers, Plantae includes all plants that perform photosynthesis, and Animalia encompasses all animals, ranging from simple invertebrates to complex mammals.