Liberalism is a political ideology often associated with intellectuals like John Stuart Mill that places a greater emphasis on individual civil and political liberties and less of an emphasis on traditional value systems.
It is worth flagging that “liberalism” has very different meanings across time and space. Today, a “liberal” in the United States is associated with the political left, and often supports robust government intervention in the economy and to support minority groups. Historically (and often abroad), “liberalism” meant supporting removing government intervention in the economy and in private life (hence “liberalizing” trade relations means removing tariffs and “liberalizing” labor markets means removing regulations). Someone who is “classically liberal” then best describes someone who is skeptical of government intervention and sharply protective of civil liberties like freedom of speech and is very much not a “liberal” in the modern American parlance.