|It doesn't stop at the water's edge:|
A liberal tends to champion liberty, individual rights and equality, although it depends on what measures are being taken to realize those rights. Due to this, liberalism can fall under many branches, some even self-contradictory; for instance, classical liberalism favors limiting government action to promote individual rights while social liberalism tends to favor government action to protect individuals. Unlike conservatism, its traditional political opposite, liberalism may be against the status quo, favoring changes to better society.
 In Europe
Europeans typically use the term to describe politics that draw on classical liberalism's basic touchstone of the individual operating in a free market economy, a notion similar to modern libertarianism. These liberals oppose government regulation on the free market to promote flow of goods in the market.
The left-wing in Europe today, however, is closer to the American interpretation of liberal. Most developed countries in the West are more left-wing than the U.S., with government playing a bigger role in general, handling universal health care, work vacations, and comprehensive sex education. The common accusations of socialism in the U.S. would've fallen face-flat in European ears, as several socialist leaders stand a significant chance or have won in elections. Not only this, but Europeans are frequently puzzled why Barack Obama is commonly called a "socialist" by his detractors.
A prominent example is the United Kingdom's politics. The UK Conservative Party would be called out as "liberals" by Republicans (or "socialist" depending on their mood) in the U.S. They support continuing the NHS while they allow abortions and same-sex marriage. Meanwhile, however, during economic recession, the party proposes spending cuts, something more in line with conservative thought in the States.
 In the USA
In the United States, liberalism is typically used to describe politics on the centre-left side of the political spectrum. Liberals tend to favor equal rights gained by government. For instance, liberals often favor the public option, gay marriage, banning the death penalty, environmentalism, increased government regulation on corporations as well as trade union presence. On other issues, to promote individual freedom, they tend to favor reproductive rights and the separation of church and state, so they may advocate secularism, removing religious symbols in public grounds, and disallowing creationism to be taught at public schools. As a result, the vast majority of liberals vote Democrat, although the party is not solidly on the left. It's probably a lesser of evils option.
The term "liberal" is used rather... liberally in the US, but most American liberals are advocates of social liberalism, which veers centre to centre-left, though it may also refer to advocates of the Third Way (If slightly to the right of social liberals) or social democracy (If slightly to their left) on economics.
Over the past few decades, the GOP has near-successfully framed it as a synonym for "socialist." This is partially due to their use of bullshit scare tactics and partially a legacy from the second Red Scare, when some people with communist sympathies, not wanting to state their affiliation openly, called themselves "liberals" or "progressives" instead. Liberalism is seen as pure evil by the Religious Right and its counterparts overseas; these groups work tirelessly to depict supporters as Satanic monsters, and to make the very word into an insult. (As a possible result of this, fewer people identify themselves as liberal compared to the amounts of self-identified conservatives and moderates, instead identifying themselves with the name of their party.)
 See also
- Age of Enlightenment, what created it
- Conservative, the traditional antonym
- Libertarian, a classical liberal on 'roids.
- Liberal Party, the various parties explicitly using the name
- Democratic Party, the US party labeled "liberal" since the 20th century and onward
- Combat Liberalism, a 1937 pamphlet published by Mao Zedong
- Neoliberalism, something liberals in the US sense seem not to like very much
- Ordoliberalism, a slightly buffered version of social democracy
- Really embarrassing liberals
- Moonbat, the much-less-flattering term for liberals. (Also used for legitimately crazy ones as well.)