This is a product that is really confusing for some people and not all brand has an emulsion in their skincare line.
Basically, one can say that an emulsion is a very light moisturizer containing more water than a regular moisturizer. Since an emulsion is light, it is easy to apply and absorbs quickly into your skin.
They normally come in a watery cream liquid, but they can also come in gel form or waterier.
They common emulsion has hydrating properties but they can still have other properties like brightening or enhancing the skin’s barrier.