Here is an example of a food web, which is made up of multiple, overlapping food chains. A food chain is the order of "what eats what," For example, plankton is eaten by krill and krill is eaten by whales. If you look at a food web however, plankton is eaten by multiple organisms, flowing into their food chains. Krill is also eaten by other organisms, making it part of multiple food chains, then in other food chains, other organisms can be eaten by multiple organisms as well making one organism part of multiple food chains. (the arrows show the direction energy flows)