The most common term I hear regarding atheism is naturalism. I'm not quite sure if that's the exact same thing as materialism.
Hmm, It took me a while to think about this. I think that whilst materialism and naturalism are quite close, there is a subtle difference. Materialism is a sufficient but not necessary condition for naturalism.
That is to say, if materialism is wrong, naturalism isn't necessarily wrong. On the other hand, naturalism would be true given the truth of materialism. Naturalism doesn't presuppose materialism.
It does seem like atheism and naturalism are conflated a lot. When people say atheism is not at all a worldview, I tend to think that's a bit disingenuous because it might be true of atheism in its purest definition but it almost always seems to imply taking on a worldview of naturalism.
This is trickier than it first looks. It not only depends upon how "atheism" is defined, but also how "worldview" is defined. If worldview is defined as a position on the conception of the world and how we interact with it, I could sketch an argument that runs counter to "naturalism being a worldview".
The tl;dr version of metaphysical naturalism is that supernaturalism is false. That's all that metaphysical naturalism entails. It doesn't say anything comprehensive on ethics, politics and other factors which may constitute a worldview. For instance, some naturalists can be moral realists whilst others are ethical nihilists. I'm not sure how one could claim to be an ethical nihilist on Christianity for instance.
If supernaturalism is false, this only tells us that certain models of morality etc.. are wrong. It doesn't necessarily tell us which models to choose from the remaining "true" ones or that truth is favourable to falsity.
Yes, naturalism can be a worldview but it would involve some extrapolation from specified metaphysical naturalism.
Nonetheless, I really laugh at those circlejerk "omgerd science therefore everything religious is stupid" anti-theists who are adamant about their position not being a worldview.