Original: It was then known as the langue d'oïl (oïl language) to distinguish it from the langue d'oc (Occitan language, also then called Provençal), whose territory bordered that of Old French to the south.
Simplified: It was then known as the langue d'oïl (Oil languages) which makes it different from the langue d'oc (Occitan language, also then called Provençal), whose territory bordered that of Old French to the south.