Often people refer to atheists as people who believe there is no god, rather that 'don't believe there is a god'. Getting down to the nitty gritty distinguishing between the two may seem awfully nitpicky, but the first definition does imply an outlook on the world that signifcantly differs from the one that goes with the other definition. And misconceptions don't make for good communication, so here goes...
"Believing there is no god", as far as defining atheism goes, is close to the mark. But atheists don't have God on their mind the way theists do, so they don't look at the world seeing "the absence of God" in things (pompeedom lalala, hmm no god here, pompeedom tralala, hmmm nope no god here either... that's not how it works). So it's "don't believe there is a God" rather than "believe there's no god". The latter is a positive claim, the former isn't one but rather a lack of a positive claim.
The so-called "strong atheist" may positively assert that there couldn't possibly be such a thing as a god, but the so called "weak atheist" simply hasn't ever encountered anything that leads them to believe there is, or might be a god, but won't claim they never possibly could in the future.
The ones that do already think there might be a god are called agnostics. And the ones that do believe there is a god who created everything, but that he has been keeping to himself ever since are called deists.
"Believing there is no god", as far as defining atheism goes, is close to the mark. But atheists don't have God on their mind the way theists do, so they don't look at the world seeing "the absence of God" in things (pompeedom lalala, hmm no god here, pompeedom tralala, hmmm nope no god here either... that's not how it works). So it's "don't believe there is a God" rather than "believe there's no god". The latter is a positive claim, the former isn't one but rather a lack of a positive claim.
The so-called "strong atheist" may positively assert that there couldn't possibly be such a thing as a god, but the so called "weak atheist" simply hasn't ever encountered anything that leads them to believe there is, or might be a god, but won't claim they never possibly could in the future.
The ones that do already think there might be a god are called agnostics. And the ones that do believe there is a god who created everything, but that he has been keeping to himself ever since are called deists.