The principle or idea that every person has the right to live as he/she chooses so long as it does not involve initiating force or fraud against another person. The N.A.P. is the principle from which the political philosophy of libertarianism
is derived, and is also similar to the wiccan
rede, "An it harm none, do what thou wilt," as well as various other spiritual teachings.
A brief explication of the Non-Aggression Principle, also known as the philosophy of liberty, can be found online at http://www.isil.org/resources/introduction.swf in the form of a 10-minute video.