Where did the food variable come from?

Where is the variable ‘food’ coming from in this exercise? It seems like it appears without definition.
thanks

It exists only in the function as the declared formal parameter. That parameter accepts any list passed to the function as a call argument. We pass in shopping_list which is referred to by the parameter name within the function. It is still referring to the same data structure, just by a different local name.

what was the purpose of print food? Deleting it yields the same result.

Please give us an example.