Illuminators are products that can be mixed with foundations or primers to give your skin extra brightness. A healthy glow in a bottle. They come in all different forms- powders, creams, etc. Most makeup brands have an illuminator in some form. They are different from highlighters in that highlighters contain more mica so they pick up more light and are only meant to be used on certain points on the face. Illuminators can be used all over. I like to mix mine with primer after applying my moisturizer and before my foundation. Sometimes on days when I'm just running errands I'll apply a thin layer of just my illuminator to give my skin a little perk up without having to apply a full face of makeup.