Liberals refers to one with liberal views, supporting individual liberty (see Wikipedia's article on Liberalism). It commonly describes someone left-wing; one with a left-wing ideology, a supporter of any of several liberal parties, and one who favors individual voting rights, human and civil rights, and laissez-faire markets (also called "classical liberal"; compare libertarian), which gives the term a broader and more practical sense than a single short definition would suggest. Taken together, these meanings present Liberals as a flexible theme rather than a narrowly technical label, covering the central idea people usually mean when they use the word while still leaving room for closely related senses that appear in real language. Liberals therefore works well as a quotation category because it can hold direct statements about the subject, figurative uses that borrow its meaning, and broader reflections that stay anchored to the same central idea. Liberals is not limited to a single rigid definition in ordinary language, and that wider range is part of what makes the category useful for grouping related material without losing the term's main sense. When used as a theme, Liberals can support serious, reflective, argumentative, or even playful quotations, provided the wording still connects back to the core idea described by the source definitions.
