Technically means those people who embrace all elements of society.

However it is more commonly used as a term for any left-winger.

A liberal, in the American sense, is one who falls to the left in the political spectrum; In other parts of the world, however, liberalism is the belief in laissez-faire capitalism and free-market systems - hence the recently coined term, neoliberalism.

Although I do not like to generalize, for the purposes of a (somewhat) concise dictionary definition, here is the very basic liberal (American sense) ideology:

Politics:
The federal government exists to protect and serve the people, and therefore, should be given sufficient power to fulfill its role successfully. Ways in which this can be accomplished include giving the federal government more power than local governments and having the government provide programs designed to protect the interests of the people (these include welfare, Medicare, and social security). Overall, these programs have helped extensively in aiding the poor and unfortunate, as well as the elderly and middle class.
To make sure that the interests of the people are served, it was liberals (or so they were considered in their time) that devised the idea of a direct democracy, a republic, and modern democracy. This way, it is ensured that the federal government represents the interests of the people, and the extensive power that it is given is not used to further unpopular goals. Liberals do not concentrate on military power (though that is not to say they ignore it), but rather focus on funding towards education, improving wages, protecting the environment, etc. Many propose the dismantling of heavy-cost programs such as the Star Wars program (no, not the film series), in order to use the money to fund more practical needs.

Social Ideology:
As one travels further left on the political spectrum, it is noticed that tolerance, acceptance, and general compassion for all people steadily increases (in theory at least). Liberals are typically concerned with the rights of the oppressed and unfortunate – this, of course, does not mean that they ignore the rights of others (liberals represent the best interests of the middle-class in America). This has led many liberals to lobby for the rights of homosexuals, women, minorities, single-mothers, etc. Many fundamentalists see this is immoral; however, it is, in reality, the most mature, and progressive way in which to deal with social differences. Liberals are identified with fighting for equal rights, such as those who wanted to abolish slavery and those who fought hard for a woman's reproductive right (see Abortion). Liberals have also often fought for ecological integrity, protecting the environment, diversity of species, as well as indigenous populations’ rights. Almost all social betterment programs are funded by liberal institutions, and government funded social programs on education improvement, childrens’ rights, womens’ rights, etc. are all supported by liberals. Basically, social liberalism is the mature, understanding way in which to embrace individual differences, not according to ancient dogma or religious prejudice, but according to the ideals of humanity that have been cultivated by our experiences throughout history, summed up in that famous American maxim: “with liberty and justice for all.”

Economics:
Using the term ‘liberal’ when speaking of economics is very confusing, as liberal in America is completely opposite to the rest of the world. Therefore, here, as I have been doing, I will concentrate on the American definition of liberal concerning economics.
Liberals believe that the rights of the people, of the majority, are to be valued much more sincerely than those of corporations, and therefore have frequently proposed the weakening of corporate power through heavier taxation (of corporations), environmental regulations, and the formation of unions. Liberals often propose the heavier taxation of WEALTHY individuals, while alleviating taxes on the middle class, and especially the poor. Liberals (American sense) do not support laissez-faire economics because, to put it simply, multinational corporations take advantage of developing countries and encourage exploitation and child labor (multinational corporations are spawned from laissez-faire policies). Instead, many propose the nationalization of several industries, which would make sure that wealth and power is not concentrated in a few hands, but is in the hands of the people (represented by elected officials in government). I am not going to go into the extreme intricacies of the economic implications of privatization of resources, etc., but will say that privatization and globalization have greatly damaged the economies of Latin America, namely Argentina and Mexico (see NAFTA).

This summation of the leftist ideology may not be 100% correct in all situations, as there are many variations on several issues and I may have depicted the current definition of “liberal” as too far to the left than it is generally accepted.
On that note, many leftists are critical of the political situation in America, claiming that the left is now in the center, as the general populace has been conditioned by institutions such as Fox News to consider “everything left of Hitler” (as one clever person put it) as radical liberalism.
I, myself, have observed that, in America, there are two basic types of liberals: those who concern themselves only with liberal policies on the domestic front, and either ignore international affairs or remain “patriotic” and dedicated to the “American way” (Al Franken, Bill Clinton, etc.)
And then there are those, despite the criticism they face from many fellow “liberals” (classified under the former definition), who are highly critical of US foreign policy, addressing such issues as Iran-Contra, the Sandanistas, Pinochet, Vietnam, NATO’s intervention in Kosovo, our trade embargo on Cuba, etc, etc. (such as Noam Chomsky, William Blumm, etc.)
Unfortunately, it seems that adolescent rage has run rampant on this particular word, and most definitions are either incoherent jumbles of insults and generalizations or deliberate spewing of misinformation (see the definition that describes the situation in Iraq, without addressing our suppression of popular revolts in Iraq, our pre-war sanctions on Iraq that have caused the death of some 5 million children, and our support for Saddam during the Iran-Iraq war, and even our post-war sale of biological elements usable in weapons to Saddam’s regime).

someone who is usually subjected to narrowminded hostility in his or her own time, but is vindicated by posterity. Many of the political figures we revere today were liberals in their own time.

A so-called "bad" thing to be before, now and probably in the future. It's been somehow turned into an attack word. What people don't realize is that no kind of progress is made without even an ounce of liberalism in your blood. Civil rights movement? Liberal from MLK Jr. Free speech/checks and balances/etc.? Liberal idea from Enlightenment thinkers. Any kind of new technology? Liberal in the sense that you want to change the existing conditions. Face it. Any kind of change, whether good or bad, is promoted by liberalism.

People who hate conservatives.

a person that appears to prefer peaceful diplomatics and minimization of violent acts, against other countries, people, etc. They SEEM to be louder in polls and how they feel about politics. All of this is based on where I have lived, therefore I may be wrong, but I don't think so. Also, if a conservative disagrees strongly with a liberal, they refer to them as a communist.

A word meaning open minded. Ironic then how the majority of Americans hate liberals and liberalism and yet claim to be a tolerant and free society. Surely some mistake...

An individual who attempts to see the bigger picture. One who questions authority, and who believes in actual freedom, not dictated freedom, as is handed down by republican politicians.

Someone who believes in affordable health care and education and not letting the poor starve and die.