The document defines key terms related to ecosystems, including ecosystem, biotic and abiotic components, trophic levels, and food webs. It explains that an ecosystem is the interaction between a living community and its non-living environment. Ecosystems have biotic components like producers, primary consumers, and decomposers, as well as abiotic components like sunlight and inorganic materials. Energy and nutrients flow through ecosystems via food chains and food webs that link organisms across trophic levels.