| We will control|
what you think with
|Here's how we do it|
Newspeak is a language that appears in George Orwell's 1984. Designed by the ruling Ingsoc regime, its purpose is to suppress thought by severely curtailing both the conceptual vocabulary and permissible grammatical structures of Oldspeak. As Orwell describes in the Appendix: "....a thought diverging from the principles of Ingsoc should be literally unthinkable, at least insofar as thought is dependent on words." 
This idea of totalitarianism taken to its logical extreme is deeply unsettling, not least for its immediate, intuitive plausibility. As with many of the novel's terms and ideas, it captured the popular imagination and has passed into modern political and cultural discourse, to be variously used, abused and confused by individuals right across the political spectrum.
 Newspeak in practice
Orwell's description of Newspeak is imperfect, but in essence he imagines language distilled to a brute functionality. Basic needs can be expressed, but beyond this, the available vocabulary is so radically compressed as to prohibit anything other than the most perfunctory description or evaluation of any given object, term or concept.
This compression is achieved by breaking down the distinction between the different parts of speech, so that all remaining words can act as both nouns and verbs. Adjectives and adverbs are formed from these noun-verb roots with the addition of -ful and -wise, respectively. Orwell offers the example of the verb to cut, purged as its meaning is sufficiently contained within the new noun-verb knife. By extension, this would lead to the elimination of verbs such as stab, slash, slice, and carve, and knifeful could replace adjectives as diverse as sharp, cutting, pointed, piercing and incisive.
Grammatically, Newspeak is simplified to an almost infantile, pre-literate degree. Irregular verb forms are suppressed (e.g. got, ran, slept = getted, runned, sleeped) and any word can be negated with the prefix un-, (e.g. good : bad = good : ungood, and presumably unknifeful would mean blunt) allowing the further eradication of hundreds of words. Emphasis is added with the modifiers plus- or doubleplus-, hence perhaps the most famous Newspeak formulation: doubleplusungood (meaning "really really bad").
 Use and abuse of the term
Newspeak has since become a term for any language that is controlled or abused in the name of political power. Some people have compared some politically correct terminology to Newspeak — this almost universally critical, comparing unfavourably with the totalitarianism expressed in 1984.
Words that describe prejudice have been compared to Newspeak. In the case of homophobia, for example, a word has been added to describe a new feeling and attitude that specifically demeaned homosexuality unfairly and unjustly. Arguably this trend continued with the addition of heterophobia — although this is really just be a right-wing re-branding of gay rights rather than a new concept. The purpose of Newspeak, however, was to reduce the number of words in the language, thus removing the ability to express new feelings or attitudes (that this probably wouldn't work in reality is not the issue). Adding words is therefore the opposite of Orwell's original Newspeak — it enables new thoughts to be expressed with new words.
A slightly more realistic application of the term to "political correctness" would be when words are banned or discouraged. This is more in line with the original principle of restricting thought by controlling language. Racist terms such as "nigger", or
dirty demeaning terms such as "cunt" are removed from the vocabulary in order to combat racism and offensive language.
 And finally...
Crimestop is one of Newspeak's less well known concepts, but perhaps the most pertinent (and funny) when discussing the various stripes of fundamentalism. It denotes a learned mental discipline: a conditioned inability even to grasp thoughts contrary to one's own belief system.
"Crimestop means the faculty of stopping short, as though by instinct, at the threshold of any dangerous thought. It includes the power of not grasping analogies, of failing to perceive logical errors, of misunderstanding the simplest arguments if they are inimical to Ingsoc, and of being bored or repelled by any train of thought which is capable of leading in a heretical direction. Crimestop, in short, means protective stupidity."