PreambleThe preamble sets forth the purpose of the Constitution.We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquillity, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.
As for Hilary Clinton, she's simply abusing the term.
The exhaustive treatment of the proper responsibilities of State and Church here is the best and most concise that I've seen on-line.