The phrase "food chain" is defined as a series of organisms interrelated in their feeding habits, the smallest being fed upon by a larger one, which in turn feeds a still larger one, etc. An animal with no natural predator is considered at the top of their food chain.
In an ecological community, the smallest member of the food chain is called the producer. Green plants and algae are producers. Producers are eaten by primary consumers called herbivores. Cattle are herbivores. Secondary consumers are called carnivores and they consume the primary consumers. Lions, wolves and crocodiles are carnivores. Tertiary consumers, also known as humans, are the top of the carnivores in the food chain. Being at the top of the food chain means that typically no other animals eat them.