From the Cambridge International Dictionaries On-line .
Libertarians are self-governors in both personal and economic matters.
They believe government's only purpose is to protect people from coercion and violence. They value individual responsibility, and tolerate economic and social diversity. Essentially, libertarianism is the simple idea that, as long as one is not hurting another, one should be free to choose whatever behaviors they desire. This generally includes things that others may disapprove of, such as gambling, viewing pornography, indulging in recreational drugs, etc. This is not to say that all practitioners of libertarianism necessarily indulge in those practices.