The Low Countries is a term used ot refer to a geographical region, especially during the Middle Ages. This region is around the deltas of the Rhine, the Scheldt and the Meuse (Maas). Today, there are Luxembourg, Belgium, the Netherlands, and parts of Lower-Saxony (in Germany) that are in the region. Sometimes, the French Netherlands (Nord-Pas-de-Calais) are included as well.
The modern Country the Netherlands has its name from there. The region was usually referred to as de Nederlanden.