langue doc and langue doïl

langue d'oc and langue d'oïl , names of the two principal groups of medieval French dialects. Langue d'oc (literally, "language of yes" ) was spoken south of a line running, roughly, from Bordeaux to Grenoble, whereas langue d'oïl (literally, "language of yes" ) was prevalent in central and N France. The two dialect groups were named after their respective words for "yes," oc having been the form of "yes" in the south and oïl (now oui ) having been used for "yes" in the north. Langue d'oc developed into Occitan , and included Provençcal, a dialect that became the language of the troubadours in the south of France. Of the langue d'oïl dialects, that of the Paris region gradually supplanted all others as the standard idiom and developed into modern French. Both langue d'oïl and langue d'oc dialects persisted, however, in some rural areas as patois, or popular, provincial speech.

langue French, = ‘tongue’.
langue d'oc the form of medieval French spoken south of the Loire, generally characterized by the use of oc to mean ‘yes’, and forming the basis of modern Provençal.
langue d'oïl the form of medieval French spoken north of the Loire, generally characterized by the use of oïl to mean ‘yes’, and forming the basis of modern French.

langue d'oîl, the language of the north of France during the medieval period, so called to distinguish it from the langue d'oc (see Proven-çal), the distinction being based on the particle of affirmation: late Latin ‘hoc ille’ for ‘yes’ became ‘o'îl’ in the North and ‘oc’ in the South. The distinction of language corresponded to a difference of culture and literature, the langue d'oîl being the literary medium of the trouvères, the langue d'oc, or Provençal, that of the troubadours.