Definitions

There are some words and terms that some are either unfamiliar with or use them incorrectly. Because all of them are pretty "Wordy", I've only shown the bare minimum needed. The links point to the full definitions.


Agnosticism

Agnosticism, in fact, is not a creed, but a method, the essence of which lies in the rigorous application of a single principle ... Positively the principle may be expressed: In matters of the intellect, follow your reason as far as it will take you, without regard to any other consideration. And negatively: In matters of the intellect do not pretend that conclusions are certain which are not demonstrated or demonstrable.

Sub-divisions of Agnosticism include;
There's Agnostic atheism
There's Agnostic theism
Along those same lines there's;
Strong and Weak
Apathetic and Pragmatic

Nones
Is a term sometimes used to refer to those who are unaffiliated with any organized religion. This use derives from surveys of religious affiliation, in which "None" (or "None of the above") is typically the last choice. Since this status refers to lack of organizational affiliation rather than lack of personal belief, it is a more specific concept than irreligion. Polls show that in the United States, "nones" are the only "religious" group that is growing as a percentage of the population


Atheism
Atheism
Atheism
Atheism is, in a broad sense, the rejection of belief in the existence of deities. In a narrower sense, atheism is specifically the position that there are no deities. Most inclusively, atheism is the absence of belief that any deities exist. Atheism is contrasted with theism, which in its most general form is the belief that at least one deity exists. While not a real definition, a common statement among atheists is that there is insufficient evidence to warrent such a belief.

Let's stick with that. The three "Atheism" links are pretty good. But there's only a general agreed definition. However, If anyone's given to masochism, an etymological analysis is HERE

Sub-divisions of Atheism include; Negative and positive atheism and Implicit and explicit atheism

What is Atheism? there's this;
1. ATHEISM is not the same as MATERIALISM (not all atheists are materialists).
2. ATHEISM is not the same as MARXISM (not all atheists are Marxists).
3. ATHEISM is not the same as HUMANISM (not all atheists are Humanists).
4. ATHEISM is not the same as AGNOSTICISM (not all atheists are agnostics).
5. ATHEISM is not the same as SKEPTICISM (not all atheists are skeptics).
6. ATHEISM is not the same as NATURALISM (not all atheists are naturalists).
7. ATHEISM is not the same as EXISTENTIALISM (not all atheists are Existentialists).
It's a quite a bit more in depth at the link

Secular humanism

The philosophy or life stance of secular humanism (alternatively known by some adherents as Humanism, specifically with a capital H to distinguish it from other forms of humanism) embraces human reason, ethics, and philosophical naturalism, while specifically rejecting religious dogma, supernaturalism, pseudoscience or superstition as the basis of morality and decision making.

Skepticism

Skepticism  is generally any questioning attitude towards knowledge, facts, or opinions/beliefs stated as facts, or doubt regarding claims that are taken for granted elsewhere.

*  Philosophical skepticism is an overall approach that requires all information to be well supported by evidence.
*  Classical philosophical skepticism derives from the 'Skeptikoi', a school who "asserted nothing".  Skeptics may even doubt the reliability of their own senses.
*  Religious skepticism, on the other hand, is "doubt concerning basic religious principles (such as immortality, providence, and revelation)"

Critical thinking

The intellectually disciplined process of actively and skilfully conceptualizing, applying, analyzing, synthesizing, and/or evaluating information gathered from, or generated by, observation, experience, reflection, reasoning, or communication, as a guide to belief and action.

Antitheism

Antitheism has been adopted as a label by those who regard theism as dangerous or destructive. Christopher Hitchens offers an example of this approach in Letters to a Young Contrarian (2001), in which he writes: "I'm not even an atheist so much as I am an antitheist; I not only maintain that all religions are versions of the same untruth, but I hold that the influence of churches, and the effect of religious belief, is positively harmful."

Freethought

Freethought or free thought is a philosophical viewpoint which holds that positions regarding truth should be formed on the basis of logic, reason, and empiricism, rather than authority, tradition, or other dogmas. The cognitive application of freethought is known as "freethinking", and practitioners of freethought are known as "freethinkers".

Freethought holds that individuals should not accept ideas proposed as truth without recourse to knowledge and reason. Thus, freethinkers strive to build their opinions on the basis of facts, scientific inquiry, and logical principles, independent of any logical fallacies or the intellectually limiting effects of authority, confirmation bias, cognitive bias, conventional wisdom, popular culture, prejudice, sectarianism, tradition, urban legend, and all other dogmas. Regarding religion, freethinkers hold that there is insufficient evidence to support the existence of supernatural phenomena.