Name for the world that A Hero Among Monsters takes place in. Two things to keep in mind is that it is rectangular, it is flat (so a map of this world is generally an accurate representation of it) and it is bent.  The World of Light is on the left side (west,) where the sun lives, and the Land of Darkness is on the right (east,) where the moon lives.  Day/night occurs as the sun and moon circle above The Map, but due to it being bent, the sunlight never fully reaches the Land of Darkness, so it's colder and even at noon it's kind of weak, and the moon's light is never enough to bring the World of Light a true night.  It's just kind of a very long dusk that breaks with sunrise.   

Title given to the ruler of a domain (e.g., a country) in the Land of Darkness (or Darklands).  Except for one or two occasions very long ago all of the Dread Lords have been wraiths. 

One of the eight races of The Map (as the world in A Hero Among Monsters is called), wraiths are non-gendered beings of tremendous magical power who are immortal (as opposed to elves, who are simply long-lived with a lifespan of 12,000 - 15,000 years.)  Wraiths can be killed although it takes considerable effort to do so and is generally only done by other wraiths. There are relatively few of them alive, around 500, and only a few dozen have achieved the title of Dread Lord, with the rest either working under those Dread Lords, scheming to take power, or hiding away to build power. 

Title given to orcs or trolls who have proven especially formidable in combat in the Dread Lord Withering Sorrows' domain.  Military structure in this domain is relatively flat so you're either a War Master, a member of his War Party, or one of the hundreds of thousands of interchangeable rabble throughout the domain.  When at war, the Dread Lord will identify War Masters as "lead" or "in charge," elevating them to something like a General and their War Party to Colonels.

There are many, many rules (none of them written and few fully understood) around who can hurt a War Master and when.  Even in open combat, War Masters (or whatever the equivalent is from another domain) generally only fight each other.  The Dread Lords don't quite understand or care for these complex protocols, especially when they lose a war just because a specific orc got killed, but they've largely given up trying to control the minutia of their servants' cultures.