1. Within political philosophy, "classical" liberalism is simply a belief in individual rights, limited government, written constitutions, and religious toleration. In this sense, both Republicans and Democrats are liberal.
2. Within contemporary American politics, liberalism is the ideology that promotes social justice and diversity, government intervention in the economy, more economic equality, expansion of the social welfare state, and concern for consumers and the environment. Democrats are typically liberal in this sense. (Ex: Sen. Elizabeth Warren).