Definition from Wiktionary, the free dictionary
- The feeding relationships between species in a biotic community.
- (idiomatic) a hierarchy
- With my promotion this month I will continue my steady journey to the top of the food chain.
Usage notes 
Because the concept of the food chain implies a feeding hierarchy proceeding upwards to a top predator, modern ecologists usually prefer the term food web, since that term allows for a more complicated system of interactions.
Related terms 
a feeding relationship between species