PEG-10 dimethicone is a polyethylene-based emulsifying ingredient. Polyethylene, which is what the PE in PEG stands for, is a type of chemistry that allows oil-in-water or silicone-in-water emulsions to be formed.
As an emulsifier, this molecule has a water-loving portion and an oil-loving portion that help keep the water and the oil phases connected to form an emulsion.
The water-loving portion of this ingredient is the PEG-10, which is a polyethylene glycol unit repeated ten times. The oil-loving portion is the dimethicone, which allows this ingredient to be multi-functional, in that it can emulsify silicone-based ingredients in addition to oils.