Liberals are people who attempt to maximize individual freedom through a system of rights under law. In the United States, the Democratic Party is the one that most often self-identifies as Liberal.
The term Liberal (capitalization implying the political use of the word) has a separate and distinct meaning from the word liberal used outside the political context. The word 'liberal' outside of politics means 'open to new ideas for progress, tolerant of the ideas and beliefs of others'.
Using this meaning, there are liberal Liberals, and liberal Conservatives, and non-liberal Liberals, and non-liberal Conservatives. Despite this confusion, the word Liberal is widely used to describe political stances.