"Flemish" in "Flemish Brabant" means that it is in the Flemish part of the former province of Brabant of Belgium. "Brabant" was an old region, the Duchy of Brabant. The word "Brabant" appears for the first time in the seventh century when the abbey of Nivelles was founded in the "pagus Bracbatensis" ("pagus" is a Latin word meaning a very small town, with only few houses).