Developed in the 18th and 19th centuries, classical liberalism is a political, philosophical, and ethical framework based on individual liberty via human rights and equal protection. Liberalism is a political philosophy or worldview founded on ideas of individual freedom, natural rights, and equality. Whereas classical liberalism emphasizes the role of liberty, social liberalism stresses the importance of equality.
Political thinkers in the 1700s were responding to the contentious issues of their time — namely the oppressive cultural and social conditions of authoritarianism and the twin totalisms of monarchies and the church. Classical liberals such as John Locke, John Stuart Mill, Adam Smith, Montesquieu and others believed that individuals ought to be free to pursue their own interests without interference from the state or other people — so long as they were not harming others, or infringing upon their rights in turn. These principles tend to require a delicate balance between respect for the rule of law, and the limiting of government power.
Liberals espouse a wide array of views depending on their understanding of these principles, but generally they support ideas and policies such as freedom of speech, freedom of the press, freedom of religion, free markets, civil rights, democratic societies, secular governments, gender equality, and international cooperation.
In a word: freedom.