Anglo-Norman is the variety of Old French (specifically, Old Norman French) spoken and written in England and parts of Wales, Scotland, and Ireland from the Norman Conquest of 1066 through roughly the fourteenth century. It was the language of the English ruling class, the royal court, law, and administration for over three centuries.
Anglo-Norman diverged from continental Norman and Parisian French over time, developing its own phonological, lexical, and orthographic features. It retained some archaic Norman forms that continental French lost and absorbed vocabulary from Old English and Latin. By the thirteenth century, Anglo-Norman was increasingly a learned and administrative language rather than a native tongue — English children of the aristocracy were learning it as a second language.
The linguistic impact of Anglo-Norman on English was massive. Thousands of French-origin words entered English during and after the Anglo-Norman period, particularly in the domains of law (court, judge, plaintiff, verdict), government (parliament, sovereign, authority), religion (prayer, sermon, salvation), food (beef, pork, mutton — from animals named in English but served in French), and culture (art, music, literature). The result is the characteristic lexical layering of English, where Germanic and Romance-origin words coexist with different registers and connotations.