Political correctness describes the alleged practice of censoring viewpoints considered disparaging to the Liberal Agenda, but more generally a movement to encourage the use of language in such a way as to avoid perpetuating past hatred and discrimination. Conservatives and Liberals use the word in nearly opposite senses.
In the United States, it is a term used seriously by some and jokingly by others, in protest of policies seeking conformance with a set of beliefs, primarily of leftists (in the United States, traditionally identified as political liberals, but also known as progressives), which encourage cultural change (especially, but not only, in the use of language), primarily to redress real or perceived persecution of minority groups and gender discrimination. The term is also frequently used by conservatives in a broader sense to characterize any of a numerous set of beliefs they disagree with, including in such areas as environmentalism or foreign policy.
With respect to the narrower sense in which this term is frequently used (which concerns minority groups), adherents of this viewpoint may feel that one should use the so-called "politically correct" (often abbreviated "PC") term "African-American" rather than "negro" or "black", to avoid offending people in that group. It can also include support for such political policies as affirmative action and multi-lingual education; some degree of support of environmentalism and opposition to capitalism are often regarded as politically correct as well. Other targets of the supposed movement include the gender-specific pronouns of English and other languages that are perceived to perpetuate aspects of male-centered culture. Some have suggested that the adherents of these linguistic changes are concerned with, in many cases, their acceptance of some form of linguistic relativism (e.g., the Sapir-Whorf hypothesis), the idea that language influences thought and culture, or even--in some sense--that it constitutes reality itself. However that is, advocates of these language changes are agreed that the proposed changes are designed mainly to treat others with respect by not using terminology that offends them.
The term "political correctness" is itself fraught with controversy. Self-described political progressives now generally reject the use of the term, primarily because it is now usually used pejoratively, particularly by opponents who consider many advocates to be overzealous. Progressives also argue that the term is essentially meaningless, on the theory that any ideological belief, not just those on the left, are "correct" to the extent that they follow from their underlying values. They would also argue that defending the victims of repression or discrimination does not itself constitute intolerance. Critics (often, but not exclusively, political conservatives) argue that advocacy of "PC" views can amount to thought control or censorship, or that it at least makes open discussion of important social issues more difficult. However, the critics of PC have themselves been accused of using the word as a kind of smear term which itself acts as a form of thought control, much in the way that red-baiting was used in the 1950s. Proponents have also been accused of hypocrisy for denouncing mainstream religions as judgmental while themslves engaging in perceived "bashing" of groups such as whites, males, corporations, and others.
One central issue in the culture wars surrounding political correctness concerns what has come to be called affirmative action. Many of those critical of so-called political correctness argue that perceived persecution of minority groups and women is enough for proponents to demand redress, even they believe that no actual discrimination or persecution has been proven to take place. The defenders of affirmative action argue that discrimination in individual cases is often subtle and hard to prove, and that affirmative action is thus necessary in order to redress this problem at a broader level. For more information, please see affirmative action.
The history of the phrase
The alleged existence of political correctness, both the movement and the term describing it, rose to broad usage in the early 1980s. In the view of one conservative commentator, Bill Lind, however, the intellectual roots and attitudes associated with PC are many decades old  and rooted in radical leftist movements. Also, in a linguistics mailing list http://www.linguistlist.org/issues/5/5-1230.html], there was discussion of the term used--sometimes quite straight-facedly--in the early and middle 1970s. Use of the terms "PC" and "politically correct" declined in the late 1990s, and the allegedly repressive political attitudes associated with these beliefs have started to fall out of favor somewhat, but it is asserted that the above-described attitudes associated with political correctness are still very strong in many universities and other institutions.
A well-known satirical take on this alleged movement can be found in the book Politically Correct Bedtime Stories, in which traditional fairy tales are rewritten from a so-called politically correct viewpoint and often reverse the roles of good and evil from those of the original version. For example, Hansel, Gretel and their father are evil and the witch is good in the politically correct version of Hansel and Gretel.
The practice of satirizing so-called PC speech indeed took on a life of its own in the 1990s, though it is no longer so popular. Part of what it is to understand the meaning of "PC" is to be familiar with satirical portrayals of political correctness, and to understand them as such. Such portrayals are often absurd overexaggerations of what actual politically correct speech looks like. For example, in an absurd and satirically overexaggerated example of so-called PC speech, the sentence "The fireman put a ladder up against the tree, climbed it, and rescued the cat" might look like this:
- The firefighter (who happened to be male, but could just as easily have been female) abridged the rights of the cat to determine for itself where it wanted to walk, climb, or rest, and inflicted his own value judgments in determining that it needed to be "rescued" from its chosen perch. In callous disregard for the well being of the environment, and this one tree in particular, he thrust the disabled-unfriendly means of ascent known as a "ladder" carelessly up against the tree, marring its bark, and unfeelingly climbed it, unconcerned how his display of physical prowess might injure the self-esteem of those differently abled. He kidnapped and unjustly restrained the innocent animal with the intention of returning it to the person who claimed to 'own' the naturally free animal, but it immediately fled his grasp, having withstood more insult and injury than it could bear.
In fact, any so-called PC speaker would be perfectly satisfied with "The firefighter put a ladder up against the tree, climbed it, and rescued the cat."