How would you describe a food chain to someone who hasn't thought about that idea before?

I would say that the food chain is an energy transfer relationship between living things that occurs when one living being feeds the other.

Explanation:

The Food Chain is the path of matter and energy that always begins with producing beings and ends in decomposers. It corresponds to the feeding relationship, that is, the absorption of nutrients and energy among living beings. We can say that the food chain refers to the process in which one living being feeds another.

The components of the food chain correspond to every living part of it. They are classified into producers, consumers, and decomposers, each representing a trophic level and a living being.