Secular
The term secular is generally used to mean "worldly, as differentiated from ecclesiastical." The term has changed meaning dramatically over time. Its original definition preserved its Latin meaning - "of an age" - as evinced in the Secular Games, or the Carmen Secularae ("Song of the Augustan Age") by Horace.
The term may be a euphemism used by atheists, since atheism generally has negative associations in the United States. Atheism actually isn't secular (common mistake) because in a secular society everyone is considered to be legally equal no matter what they believe in or don't believe in. Atheism is a religious point of view that God(s) do not exist and is therefore not all inclusive.
The United States was founded as a secular republic, where religious freedom is affirmed in the Constitution and where no special religion is established. However, 'secular' here is not a synonym for 'atheistic' as secular society includes both Atheists and believers.
Further reading
- Emmet Kennedy, "The Tangled History of Secularism," Modern Age (Winter 2000) Volume 42, Number 1; online edition