In politics, the term liberal refers to:
an adherent of the ideology of liberalism —an ideology espousing liberty. The inverse of liberty is tyranny.
(Note: the words "liberal" or "liberalism" can have different meanings in different countries and may also vary with the political background of the user. Therefore, the term may have slightly (or vastly) different meanings. A more comprehensive discussion can be found at Liberalism.)
a political party associated with ideals of individual freedom, greater intellectual liberty, greater individual participation in government, and constitutional, political, and administrative reforms designed to secure these objectives, such as the U.S. Constitution. The political opposite of a liberal is either a conservative or a socialist, depending on who uses the term.
if capitalized (as in Liberal with a capital-L), the word usually refers to members of a political party that goes by the name Liberal Party (Note: a party calling itself Liberal may not necessarily follow what some people consider to be Liberalism.)
a supporter or member of a liberal party (see also small-l liberal).