I wish to begin by saying that no definition of Liberal can be found without some personal bias of the author. I myself am a liberal, and although I believe this to be a comprehensive definition, others will define Liberal in a more callous sense. They are mistaken, but that's just my opinion. "Baby killer", for instance, is merely a stereotype of a liberal.
Of the left wing in the political spectrum; liberal is a broad term usually lost in the flurry of stereotypical distinctions like Democrat, Anarchist, Libertarian, Green, or Socialist. Liberals typically value personal freedom and the well-being of others over their own moral opinions. Liberals have been the moving force in American culture for centuries, with the conservatives being the holding force. Liberals were responsible for the emancipation and suffrage of blacks, women's suffrage, the teaching of evolution, and other political decisions considered controversial by the right. Atheists are typically associated with the left, as are gays, blacks, "pro choice" proponents, and American intellectuals. It is confusing to associate either liberals or conservatives with America's financial base, because both sides have wealthy families. America's religious base is more commonly aligned with conservatives, and thus most attacks on liberals are fueled by religious fervor (criticizing liberals on being pro-choice on abortion, on not supporting the War in Iraq, on calling for stricter enforcement of separation of church and state, etc). In recent years, there have been few good representatives of Liberalism, those few being Michael Moore, Howard Dean, John Kerry, and a handful of relatively unknown writers and artists (Howard Zinn, Zach De La Rocha, etc).
Why do conservatives call liberals "commies", even though communists are conservatives themselves? Is it too hard to say "socialists"?