An agnostic believes that people cannot know if God exists, and an atheist lacks belief in God. An agnostic accepts the possibility that God may exist but states that people cannot know at the present time whether he does or not, while an atheist takes the bold stance that God does not exist.
Biologist Thomas Henry Huxley created the term "agnostic" in 1869 to differentiate his doubts about God from the atheist belief that God does not exist. Charles Darwin and popular anti-religious lecturer Robert Ingersoll also labeled themselves agnostics during the same era. Some ancient Greeks doubted the existence of gods because they could not prove the gods' existences through scientific testing.
The term "atheism" comes from the Greek "athos" meaning no gods. The first modern people to label themselves atheists appeared during the Age of Enlightenment in the 18th century. American Atheists states on its website that atheism is not a belief system but that some religions are atheistic, such as some Buddhist sects. American Atheists further describes that atheism is a lack of belief in gods and other supernatural beings, rather than a disbelief in gods. Atheists have a variety of convictions and beliefs. The Pew Research Center's 2014 Religious Landscape Study found that 3.1 percent of U.S. adults label themselves atheists, an increase from 1.6 percent in 2007.