An "ecosystem" refers to a community of living organisms interacting with their physical environment. It includes all the biotic (living) factors, such as plants, animals, and microorganisms, as well as abiotic (non-living) components, like water, air, soil, and climate. Ecosystems can vary in size and complexity, from a small pond to a vast forest or desert. The interactions within an ecosystem are crucial for nutrient cycling and energy flow, ultimately supporting biodiversity and contributing to the overall health of the planet.