Libertarian is a party and a legitimate political classification. Of course, like the Green party and other semi-popular third parties, they stand little chance of being elected to most major offices, though there are reportedly some scattered around minor offices.
They generally believe in individual rights, personal responsibility, and generally leaving other people alone if they aren't harming someone's rights to life, liberty, and property.
One of their more controversial positions (esp. among gun owners) is the opposition to the war on drugs. The libertarian position is that restricting what adults can do to their bodies is unconstitutional and wrong, and that the war on drugs is a gigantic waste of money and an excuse for limiting our rights.
They also generally oppose welfare, social security, and things like that in favor of a pure capitalist economy.
They are also the only party to my knowledge that opposes all gun laws.
I tend to agree with them on most things, but some of their members take positions that I do not agree with. These generally involve the millitary, foreign relations, and things like the War on Iraq/War on Terror.
Feel free to investigate and ask more questions.