Here are a few cuts to get the definition process started (emphasis mine):
"Naturalism" refers to a number of different topics:
As defined by philosopher Paul Draper, naturalism is "the hypothesis that the physical world is a 'closed system' in the sense that nothing that is neither a part nor a product of it can affect it." More simply, it is the denial of the existence of supernatural causes. In rejecting the reality of supernatural events, forces, or entities, naturalism is the antithesis of supernaturalism.
As a substantial view about the nature of reality, it is often called metaphysical naturalism, philosophical naturalism, or ontological naturalism to distinguish it from a related methodological principle. Methodological naturalism, by contrast, is the principle that science and history should presume that all causes are natural causes solely for the purpose of promoting successful investigation. The idea behind this principle is that natural causes can be investigated directly through scientific method, whereas supernatural causes cannot, and hence presuming that an event has a supernatural cause for methodological purposes halts further investigation.
Drange: Atheism, Agnosticism, Noncognitivism (infidels.org) Suppose you are to answer the following two questions:
Most scientists I know don't care enough about religion even to call themselves atheists.
I call myself an atheist because I do not practice a religion, don't pray (even in dire straits), and my mental pitcure of the universe does not include a deity. I don't do any of these things because in my experience religious practice is a waste of time, I see no evidence that prayer by me or anyone else works, and because a deity has no explanatory or predictive power. Atheist is a short and reasonably accurate label. If a supernatural being appearted tomorrow and said 'Hi, I'm God', having discounted trickery and hallucinations I'd certainly change my view, though I'd be more inclined to study said being than worship him. You can call this agnostic or atheist or anything you want; I don't see anything fruitful in a discussion about the particular mode in which people don't believe in a deity.
Christianity has entertained itelf for two millenia by dividing itself into hundreds of feuding sects, often based on the most idiotic minutiae of doctrine; but Christians shouldn't assume that the non-religious share the same fascination with hair-splitting about the ineffable.
I'd avoid discussion of religion altogether if religious people stayed out of my space; if they stopped trying to force their supernatural ideas into science; and if they stopped denigrating those who don't happen to share their view of the Universe (e.g. by asking if 'atheists can be intellectually fulfilled', by suggesting that atheists are inherently amoral, etc.). My parents were, and one of my brothers' wives is religious; I don't denigrate their beliefs, and I respect their intellect. I don't go asking if their Christianity is attended by some intellectual defect. Why are so many religious people unable to muster up the same level of tolerance?