Any view holding that things in general, or things in some sphere under investigation, are all of one kind (as opposed to being of radically different kinds), and are amenable to study by scientific methods, without appeal to supernatural intervention or special kinds of intuition. In art or literature, any of a variety of views saying the artist should imitate the natural world or actual human behavior.
In recent philosophy, naturalism has usually taken the form of an ethical theory, denying the fact/value distinction, and also denying that ethical facts are sui generis in nature; those ignoring either of these denials are said to commit the naturalistic fallacy.
Ethical naturalism is akin to, but not identical with, descriptivism (George Edward Moore (1873-1958) was a descriptivist but not a naturalist).
P Foot, ed., Theories of Ethics (1967)