Flavoring oil is simply the oils from the fruit or nut squeezed out. Like in this recipe since I was making strawberry frosting, I used Strawberry Super-Strength Flavoring. It really accentuates the strawberry favor. If you've never tried using Flavoring Oil before, you really should. The key when using the oil though is to add a little bit at a time to make sure that it's not overpowering.