Well a recipe item is an item that represents a recipe. If you have played video games with alchemy-like features, you will know that some of them only allow you to mix items if you have the recipe. So if an alchemy combination requires a recipe, you cannot mix items this way unless you have the recipe. For instance, if the alchemy of A + B -> C requires a recipe, you cannot make C from A and B without having this recipe in your inventory. Maybe its not a good explanation, but hope you understand what I mean.