A food chain is a sequence of organisms in which each one feeds on the previous one, and is itself fed upon by the next higher level. In other words, it's an interconnected network where different species rely on each other for survival through feeding relationships. The sun provides energy to plants, which are then eaten by herbivores, who in turn are consumed by carnivores. At each step of the chain, a certain percentage of the available energy is lost as heat or excretion, so only some of the energy from one level up is passed on to the next higher level.