Manufacturers of Detailing related products
The refractive index is a way of measuring how lights behaves through a certain medium. This number gives an indication of how light reacts and how light is reflected. Manufacturers use (among other things) this as an indication of how light is reflected by a protective product and how that will make the surface look.
Paint, just like any solid surface, has a certain hardness. To put it really simple, this tells you the force needed to put a scratch in the surface. Very soft paint gets marked easily, but is also easier to polish. A hard surface might not get scratched as easily, but will also be more difficult to polish.