I think that was just jack referring to the continent as “northwestern” which is highly relative depending where on Athas you are lol
Rema(a)n (I’ve tended to add another A to as Reman tends to conjure star trek nemesis flashbacks XD) is specifically the continent in the northwestern corner of the Steve Bell/ACG globe maps. The southern one is not Remaan, it an entirely separate continent never or only sparsely inhabited by the Rebirth Races. Like the rest of the greater world, Remaan is entirely fanon- the earliest use of it I can find of it is from the netbook Last Frontier as “Remani.” Peter Nutall (Brax), who was one of the main people working on Secrets of the Dead Lands and Lost Cities of the Trembling Plains, greatly expanded the names from said netbook- Melai, Tanysh, and Reman, into the larger-scale human cultures of Green Age Athas, with Wisdom of Sorrow being the most prominent case. Brax laid some basic ideas for the continent’s current state in his old sitechttps://urbraxa.tripod.com/AthasianPhoto.htm, which I’ve used as a base for my own take on Remaan.
The basics are that “Remaan” was not just a human culture, but a “creed” based around inter-rebirth race unity and cooperation, with each race occupying an “ecological niche,” and encouraging peace through trade, kinship ties, ect. They resurrected the old Rhulisti “Lawgiver” system and developed the Athasian “Great Pantheon” which was a collection of ancestral folk heroes, spirits, gods, ect, all as aspects of the four major elemental cults (for example an orcish fertility goddess would be associated with earth and was probably based on an actual spirit of the land or elemental lord). Their systems migrated back to the tablelands with Remaan colonists who resettled places like Balic and Tyr, and became the de-facto global model for politics, culture, religion, and language.
Based on Wisdom of Sorrow, Remaan started as the only multiracial tribes to emerge out of the Rebirth and were actually descended from the angry crowds who seized the Pristine Tower and willfully mutated to be with their loved ones. “Remaan” is probably a linguistic artifact of a rhulisti term for “We stand together!” like a protest chant. They fled the Tablelands when the human-supremacist Tanysh flooded out of the north like a plague, and settled the distant continent both for safety and also to get as far away from the Pristine Tower and rotten legacy of the Nature-Masters as possible. They took a lot of Pyreen with them, as the Remaans were entrusted with care of the first baby Pyreen. Eventually the roles reversed with the Pyreen being the “guardians” of the Remaan peoples and showering them with favoritism. Remaan culture focused on long term stability out of a fear of a repeat of the Blue Age, and locked Green Age into its millennia long psionic stagnation with massive inequality, and left populations as kindling for Rajaat and the Age of Magic.Think of them as a sort of archaic, psionic form of global neoliberal hegemony 
While nominally the “good guys” their was rife with hypocrisy- be it favoring the first five member races (Human, Elf, Dwarf, Orc, Pterran) to having extremely wierd bioessentialist views that each race was “ideally” suited for a certain role (Humans are herders, orcs are farmers, elves are sailors, ect) with the endgoal basically being hybridizing all of them out of existence into hybrid races like half-elves, who were free of the “sins of the rhulisti.”
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