i dont get it. what "art" means here?

I think an Art is like a Familiar or the human that represents a vampire in some vampire tropes.

Just me guessing here, but maybe art stands for a rich taste ;)

Arts are pretty and tasty humans that can be pets/playthings to a vampire. I think the word "art" is chosen because they have to be beautiful, like a work of art. That's at least how I understand it.

Refined Escort = piece of art = Art
More fancy that use "whore" or "sex slave"

I think Art refers to highest grade of humans. Great looks and top notched blood, not to mention rare eye colors. Sort of like pet to vampires to show off their status