Defining Atheism

When I look back at my first encounters with definitions of atheism I am astounded at how difficult it is to get across the basic concept of what atheism is. Theists have managed to muddy the waters to a degree that even actual young atheists are confused by it. Yet it is actually very very simple in principle.
I think one reason why some apologetics distort it's meaning is because only a distorted view of the stance is really something that is hard to defend.

So what is atheism from the point of MOST atheists, including the major thinkers like Hitchens, Dennett, Dawkins and Harris.
It's a lack of belief in god or gods. That really is the broadest brush on the topic.
However there are subsets of atheistic views that can be held by particular atheists and those views can include disbelief in gods, rejection of claims about gods, belief in no gods and even the old and often misapplied belief that no gods exist.

Lets look at how 'atheism' is constructed to fully grasp my point. Theism existed as a stance and from it atheism was coined. Now once it was coined (put in use) it can be applied retrospectively to cover people that lived BEFORE theism, but it is not its OWN label, but a reaction TO theism.

So lets break it down. 'THEOS' means god. That is usually accepted. 'ISM' refers to a belief.
So THEISM means Belief in a god or gods. Nowadays it might be more accurate to stick 'personal' into that to distinguish between theism and deism but that is beside the point for the moment.

Ok, now add the 'A' which is best explained as 'without'. So A-THEISM means 'without' belief in a god or gods.

This does not mean that atheism means belief that NO GOD exists. This is a distortion of how the word was developed as it ignores the history behind why it exists.

Now in practical terms what does all that MEAN? Well from my perspective it means we don't believe the claims made by theists that propose they know a god exists and they have some knowledge about what it wants. You might note that I solely focus on the CLAIMS about god, not the actual question of whether a god actually exists.

A good analogy might be if someone (John for argument sake) disbelieves in alien abductions when he hears his neighbour (Peter) claim he sees them when he is blind drunk walking back from the pub. Does that mean that John knows aliens don't exist or that they cannot have visited earth to do some nasty abductions? No. But the claim by Peter is so poorly supported that you doubt his veracity and credibility and so you put the thought of alien abductions out of your head and live your life as if it was never a consideration. If Peter came back with verifiable proof that he got from the aliens, (see N.D. Tyson's amusing talk on what to do if abducted by aliens) then John would reconsider and re-evaluate whether the NEW evidence is enough to sway him on the matter.

Why is there so many different definitions for atheism if its simply a lack of belief in gods?
Again this is often a simple misunderstanding. Atheism is the lack of belief in theistic claims, but there are many avenues that an atheist can approach that situation.
For instance there is often comments about babies being atheistic, but how can they be atheistic if they had not the ability to reject theistic claims. Well because the definition at its broadest is a LACK of belief and babies certainly qualify for that level of atheism. This is referred to as implicit atheism
Explicit atheism is when someone is aware of theistic arguments and rejects or disbelieves them.
This covers almost every atheists anyone is likely to meet and is generally how most atheists discuss atheism. But to be fair, BOTH stances are atheistic, just the approach is different.

Does any atheist say they know there is no gods?
I hear that a lot from theists, but there is often a rather selective hearing issue involved. It is possible to say "I believe God does not exist" and not mean any possible definition of god, especially vague nonreligious ones. In many cultures an atheist may simply assume you mean the abrahamic God (capital letter intended) and that is what he or she is referring to. Most theists of that presuasion only think about that God anyway so there is justification in answering like that. However some people take that and run with it as if all atheists MUST know somehow 100% that nowhere in the universe and beyond some form of higher intelligence could not exist or they are not atheists. This is of course simply a strawman view and I have never met any atheist that thinks such a view is even rational.
Even the most famous atheist on the planet, Richard Dawkins, repeatedly refutes this flawed view over and over again.

Atheism vs Agnosticism: Is there any link?
Frankly I find this truly amazingly misunderstood by all three 'sides' (those that call themselves atheist, those that call themselves agnostic and those that call themselves theists).
Huxley was the man responsible for coining Agnosticism and it was to cover the question of whether it was possible to know if god (no capital letter) can be verified empirically existing or not. If not, then you remain 'agnostic' or undecided about it.
However this has NOTHING to do with theism or atheism which address claims ABOUT god not whether god actually exists objectively.
Every agnostic still has to either accept or reject any theistic claim on its own merit. Even if you don't explicited reject it if you DON'T accept it you have rejected it in any practical sense.
So its possible to be both agnostic AND atheistic or theistic as they cover two different questions.
Nowadays many theists and atheists accept the following groupings.
gnostic theist = someone who knows that god exists and believes in that god.
agnostic theist = someone who does not know that god exists but believes that he might exist.
agnostic atheist = someone who does not know that god does NOT exist but disbelieves claims that he does.
gnostic atheist = someone who does know that god does NOT exist and disbelieves claims that he does.

Its perfectly acceptable to be a gnostic atheist about SOME gods (Zeus or Horus or Allah or Jesus) while being an agnostic towards poorly defined possible gods. After all it would be irrational to expect someone to have only ONE view on every possible god.