Oddly enough, this thread came to my attention while I was eating breakfast...cornflakes & milk with molasses. I use it as a sweetener for cereals pretty often (mostly because the milk is so delicious at the end).
In Spain spanish, I grew up understanding this as comparable to the difference between "beef" and "cow," or "pork" and "pig."
Pollo is edible chicken, gallina is a hen, the whole animal.
I had no idea there was a class of food that used the word "gallina."