Maas is the name, in English borrowed from the Dutch language, of a river that is also named Meuse (river), in English borrowed from French language. The practical use in English may be influenced by the context at a lower or upper stream location.
Maas is a Dutch and North German surname. It is the modern (after 1804) northern Dutch spelling of the name Maes due to the standardisation of the northern Dutch spelling under Matthijs Siegenbeek.