What is non-naturalism?

I really don't have a firm grasp of this concept.

If one is a non-naturalist about ethics, then this means that one thinks that ethical properties are not natural ones. Well, what's a natural property? Attempt one: it's a property in the universe. Well that's not helpful! That just means that a non-natural property is one that doesn't exist (because I assume that the universe is just the class of all things that exist). OK, so maybe the natural properties are the ones studied by scientists. By that definition I suppose that a lot of properties that are physical could be non-natural ones. So maybe the natural properties are the ones that could be studied by scientists. What's the point of this definition; is the point just that scientists are able to study properties that can be found in space, are physical? So then all it means to be non-natural is to be an abstract object? That could be, but that doesn't pick out anything but abstract objects, obviously, so it's superfluous terminology.

I can think of two other definitions of non-natural properties. I need to read more so that I have a firmer idea of what it means. One definition would be that it is relevant for scientific explanations, or indispensable to explanations. This merges the natural properties with the ones that are derived from IBE, obviously. Again, not so interesting, but possible. The second definition is that the non-natural properties are those that we have to take as primitive. This won't quite do because then you'll have some physical properties that are non-natural. Grr. Not really sure what to do here.