It's a belief based on evidence. That's the difference. It's the way you you should decide what you believe about everything.
There are a large number of religious people who argue that Atheism is a belief, as though this some how brings down Atheism to the level of religion. It doesn't. Religion is "faith", which is belief without evidence.
Having beliefs is not the problem Atheists dislike. Having irrational beliefs is the problem.
I believe the sky appears blue most of the time, because I can see it, and it's fucking blue.
I believe water changes state from solid to liquid at room temperature, because I can leave an ice cube in a room and watch it melt (boring as bat shit though).
I believe there is no god, because I decide what to believe based on evidence, and there is insufficient evidence to warrant a belief in god.
Some say "absence of evidence is not evidence of absence", however this simply not true. There are circumstances where a lack of evidence does lead to proof of absence.
For example if someone tells you there is an elephant on your front lawn, and you look and see no elephant, or no evidence that an elephant was there (RE: the elephant would have left a trace on the lawn), then you can assert that there is no elephant on your front lawn.
Technically, because of the way humans continually redefine god, it is impossible to disprove it. Thus technically I should be an agnostic, saying there is not enough evidence either way. However technically, I can't prove there is no santa, no unicorns, and no bigfoot.. but I'm pretty fucking sure they don't exist either.
Atheism is a belief. Beliefs aren't the problem. Beliefs not based on evidence, or beliefs based on incorrect reasoning are the problem. Beliefs because of evidence and reason - all good.
If you want to say you have "no beliefs either way", call yourself an apistevist, not an atheist.