The lowland region of western Europe on the North Sea: Belgium and Luxembourg and the Netherlands WordNet 3.0 & Open English WordNet

The European region known as the Low Countries, historically once also known as the Netherlands, Flanders, or Belgica, is a coastal lowland region in Northwestern Europe forming the lower basin of the Rhine–Meuse–Scheldt delta and consisting today of the three modern "Benelux" countries: Belgium, Luxembourg, and the Netherlands – which English and French give the same name as the traditional regional name. Wikipedia

A historical region in Europe, although rarely used in this context Wikipedia Disambiguation

Historical coastal landscape in north western Europe Wikidata

The countries on low-lying land around the delta of the Rhine, Scheldt, and Meuse (Maas) rivers. Wiktionary

Countries around the Rhine, Scheldt and Meuse rivers. Wiktionary (translation)