Food Chain: Afood chain is the sequence of energy transfer from the lower trophic levels to the upper or higher trophic levels in a natural ecosystem.

Trophic Levels: The levels through which food energy passes from one group of organisms to the other group are called trophic levels.

Energy Pyramid: The pyramid, representing total amount of energy used at each trophic level of food chain in a natural ecosystem, per unit area per unit time, is called energy pyramid.