Atheism can be either the rejection of theism ,  or the position that deitiesdo not exist .  In the broadest sense, it is the absence of belief in the existence of deities . 
The term atheism originated from the Greek ?θεος (atheos), meaning "without gods", which was derogatively applied to anyone thought to not believe in the accepted gods, or to believe in false gods, no gods, or doctrines that stood in conflict with established religions. With the spread of freethought , skeptical inquiry , and subsequent increase in criticism of religion , application of the term narrowed in scope. The first individuals to self-identify as "atheist" appeared in the 18th century. Today, about 2.3% of the world's population describes itself as atheist, while a further 11.9% is described as nontheist .  Between 64% and 65% of Japanese describe themselves as atheists, agnostics, or non-believers,   and up to 48% in Russia.  The percentage of such persons in European Union member states ranges between 6% (Italy) and 85% (Sweden). 
Atheism tends towards skepticism regarding supernatural claims, citing a lack of empirical evidence. Common rationales include the problem of evil , the argument from inconsistent revelations , and the argument from nonbelief . Other arguments for atheism range from the philosophical to the social to the historical.
In Western culture , atheists are frequently assumed to be irreligious or unspiritual.  However, religious and spiritual belief systems such as forms of Buddhism that do not advocate belief in gods, have also been described as atheistic.  Although some atheists tend toward secular philosophies such as humanism ,  rationalism , and naturalism ,  there is no one ideology or set of behaviors to which all atheists adhere.