Nadsat is a fictional register or argot used by the teenagers in Anthony Burgess's novel A Clockwork Orange. In addition to being a novelist, Burgess was a linguist and he used this background to depict his characters as speaking a form of Russian-influenced English. The name itself comes from the Russian suffix equivalent of "-teen" as in "thirteen" (-надцать, -nad·tsat'). Nadsat was also used in Stanley Kubrick's film adaptation of the book.
Nadsat is a mode of speech used by the nadsat, members of the teen subculture in the novel A Clockwork Orange. The antihero and narrator of the book, Alex, uses it in first-person style to relate the story to the reader. He also uses it to communicate with other characters in the novel, such as his droogs, parents, victims, and any authority-figures with whom he comes in contact. As with many speakers of non-standard varieties of English, Alex is capable of speaking standard English when he wants to. It is not a written language: the sense that readers get is of a transcription of vernacular speech.
Nadsat is basically English with some borrowed words from Russian. It also contains influences from Cockney rhyming slang, the King James Bible, the German language, some words of unclear origin, and some that Burgess invented. The word nadsat is the suffix of Russian numerals from 11 to 19 (-надцать). The suffix is an almost exact linguistic parallel to the English '-teen,' and is derived from "на", meaning "on" and a shortened form of "десять", the number ten. "Droog" is Russian друг "close friend". Some of the words are also almost childish English such as eggiweg ("egg") and appy polly loggy ("apology"), as well as regular English slang sod and snuff it. The word like and the expression the old are often used as fillers or discourse markers.