Cetearyl Alcohol is a mixture of stearyl and cetyl alcohols. It's a wax derived from vegetables and it can also be made synthetically.
Cetearyl alcohol is considered a "fatty alcohol." It's mainly made from coconut or palm. Fatty acids (such as cetyl and behenyl alcohol) are used to thicken formulas and emulsify oil into water.
While alcohol in skincare is best to stay away from because it's drying, these fatty alcohols actually help condition, which is why it's a popular ingredient in skincare and haircare.