Irreligion (adjective form: non-religious or irreligious) is the absence, indifference to, or rejection of religion. According to the Pew Research Center's 2012 global study of 230 countries and territories, 16% of the world's population is not affiliated with a religion, while 84% are affiliated.
There are many forms and subsets of irreligion, ranging from the casual and unaware to full-fledged philosophies such as secular humanism. Varieties include atheism, agnosticism, antitheism and more. Being objectively irreligious, as delineated in social sciences, is basically adhering to a purely naturalist worldview, without influence from supernatural faith. The broadest definition is lacking religious identification, though many of the non-identifying express various metaphysical beliefs, and the narrowest and strictest is positive atheism. The global demographics of irreligion are estimated based on the former as maximum, and the latter as minimum, therefore ranging between 450 million to 1.6 billion people. Measuring objective irreligiosity requires cultural sensitivity, especially outside the West, where the concepts of "religious" and "secular" are not rooted in local civilization.