What is Atheism?

[FatAndFaithless]

A lack of belief does not require a burden of proof, because a lack of belief is the default position when there is a lack of proof and valid arguments to sufficiently justify a knowledge claim. Knowledge claims require proof. Lacking a belief in something is not a claim (because knowledge, which is justified true belief, is a subset of belief) and therefore does not carry a burden of proof. We must start with a lack of belief as the default position, because otherwise we will end up believing things that have not met their burden of proof.

In terms of what is actually true, are only two possibilities: a god exists, or a god doesn't exist. Atheism and theism only address the former claim. Theists believe this claim, and atheists do not. Atheists lack a belief in the claim "a god exists" because it has not met its burden of proof.

Also, having an opinion about "x" not mean you have a belief in "x". To believe something is to become convinced that it is true, which is not a prerequisite for having an opinion about that something.

Right.  And simply saying "I do not believe your claim has met its burden of proof" does not carry a burden of proof of it's own...because it's literally just stating that you don't find a claim convincing.

Careful though, you'll quickly note on here the people that love to spin their wheels in the semantic mud and never get anywhere in a conversation.