Definition of "atheism"

[Pyrrho]

Could any form of theism ever be stated as a lack of belief? ...

Every form of theism involves a belief in the existence of at least one god.  That is the minimum requirement to be a theist of some kind.  There is no additional doctrinal requirement to be a theist.  Of course, to be a particular type of theist, like, say, a Southern Baptist Christian, then there are more requirements than just belief in the existence of at least one god.  But all people who believe in the existence of at least one god are theists.

For more on these topics:

http://en.wikipedia.org/wiki/Atheism

http://en.wikipedia.org/wiki/Theism


Edited to add:

Weak atheism, which is going along with definition 2 in my original post (post # 1) but not going along with definition 1, is contrasted with strong atheism, which is going along with both 1 and 2.  Definition 1 "contains" or entails 2.  That is, if one has the belief that there are no gods, then one lacks a belief in a god (if, that is, one is consistent and does not believe incoherent contradictory things).  The reverse, of course, isn't the case; lacking a belief in a god does not entail the belief that there are no gods.

Definition 2 is essentially meaning, "not theism."  Definition 1 goes beyond that, and affirms that theists are wrong.

A weak atheist is not a theist, but does not claim that theists are wrong to be theists (though they could believe they are wrong to be certain specific types of theists, such as Southern Baptist Christian or whatever).  A strong atheist claims that theists are wrong, no matter what type of theism we are talking about.