What's a libertarian?

I've heard that term "Libertarian" before. What does it mean?
Libertarianism is a view that upholds liberty as its principal objective. In other words, when something in society is done, libertarian-minded people generally want it to be done in a way that respects, or even increases, everyone's freedom. 

Libertarians are also often interested in things like maximizing autonomy and freedom of choice, emphasizing political freedom, voluntary association, protecting individual judgement, property rights, and privacy.

Self-described libertarians don't fit well into preconceived labels. Two libertarians might vigorously disagree on issues of society, politics, religion, and other things, but they'll rarely disagree that mankind prospers best when it's free to choose its own path.