A patois is a regional dialect, which is different from the standard or literary language. A synonym of patois is jargon. It comes from the French patois, which means local speech.
I asked for a few words in patois. Mr. Gex said that words for the same thing can differ not only from one valley to the next but even from one village to another within the same valley, though each can understand the other. (NY Times)
Plans to translate the Bible into patois — Jamaica’s unofficial language — have ignited a fiery debate that stretches beyond the shores of this island nation. (USA Today)