The expression, Novus Ordo Seclorum, contrary to urban myth does not mean 'New World Order' but actually translates to 'A New Order Of The Ages'.
It is used in the novel Cryptonomicon as the name of a piece of cryptographic software, a play on words as the software scrambles messages i.e. puts them in a new order.
Following the Declaration of Indepedence the phrase was chosen to signify the new world the founders wished to create free from tyranny and oppression. It can be seen in the Great Seal of the United States below the pyramid of the thirteen stones representing the original colonies.