Edible vs. Non-Edible

Question

What are the Halachic definitions of something that is "Rauy l'achila" (fit to be eaten), versus something that is "Aino rauy l'achila (NOT fit to be eaten?). If something that is NOT fit to be eaten (aino rauy) is an ingredient in a kosher food product, how is that ingredient "aino rauy" if it can be eaten with things that are "rauy"? Is it that an ingredient must be edible, and indeed, eaten by itself to render it "Rauy l'achila"? No one in the world sits down to a hot cup of carmine coloring?