I believe essence works just like a serum and they just name it differently. A two-in-one essence toner means that you can easily put in on a face cotton and wipe your face to simultaneously clean, tone, and enrich/moisturize/brighten/etc (depending on what the essence does) your skin all at the same time while wiping your face. Normally, you will have to first tone then apply the essence for better absorption but I guess that product make your life a bit easier. I personally a bit skeptical about this product as I want an essence that specifically made for its job and worry that that the efficacy would have been reduced since they also mix a toner formula inside that is known to simply clean and tone the skin. It is best that you check the review of the product first from cosmetics review websites before you buy it.