Cover of the 1st book in the series
The Mer is a species of people that live underwater - or specifically, Ingo. Pure Mer tend to have a bluish tinge to their skin. Most Mer dislike humans for everything they have done to the ocean and some even want Ingo to cover the whole world.
The Mer are known by many names, including Mor, Meor, and More. They call themselves 'neshvyn lowenna', which means the 'happier kind' (or just 'lowenna', which is 'happier') in their language, which is also called Mer. In the 4th book after the war Saldowr says that they may have to stop using that name seeing as they are not in peace.