Atheism, in its broadest sense, is an absence of belief in the existence of gods. This definition includes both those who assert that there are no gods and those who make no claim about whether gods exist or not. Simply stated, anyone who does not say "I believe (a) god/gods exist," is, by definition, an atheist. Narrower and more common definitions, however, often only qualify those who assert there are no gods as atheists, labeling the others as agnostics or simply non-theists.
There is no single ideology that all atheists share, nor are there any institutionalized rituals or behaviors. There are certain individuals whose religious or spiritual beliefs some might describe as atheistic, though those holding such beliefs do not normally describe themselves as atheists.
Due to some contrary belief, primarily in heavily religious countries, being an atheist does not imply deliberately "disobeying God". Atheism is not a belief but is only the absence thereof. Atheists are also sometimes accused of "hating God", which is impossible since you can not hate something you do not believe exists. Atheism is not directly linked to evolution, nor the big bang theory. However, many atheists, primarily those who wish to study atheism and religion further, turn to science, hence gaining an interest in such theories.
In countries such as the United States of America and continents such as Asia, religion is thriving. Although it may seem black and white, countries with the highest poverty and murder rates, lowest education rates and human development rates (HDI), tend to be the most religious, in contrast with the most atheistic countries, such as Norway and Sweden. This can also be observed in the US by state.