First time readers can get confused about these two terms. Not surprising, given the main character Bret is also not that clear on the difference when the books begin. Let’s talk about the differences and touch on a view important elements of Eschatos Diagram along the way.
Realms
The Eschatos Diagram is, for all intents and purposes, a giant map. A very decorated and intricate one that covers the cosmos, but a map, nonetheless.
The building blocks of the Eschatos Diagram are Realms, which can be understood as a zone or region of Cosmos. Before the creation of the Eschatos Diagram, Realms existed as autonomous sentient zones that grew out of Oikumene, the unity of nothingness.
Before the Eschatos Diagram was inscribed, the physical definition of a Realm was fluid. Crafting the Eschatos Diagram fixed borders into place, framing them in a physical and metaphysical way.
So, a Realm represents a physical portion of the cosmos and a sentience, which is referred to as a “world consciousness”.
The size and components of a Realm define its strength. Realms are defined as mega-realms, Realms, and micro-realms.
Mega-realms have diverse, high functioning worlds and contain systems and physical elements that create large amounts of Providence. They contain few, if any nebulae or scars, such as black holes.
Realms fit somewhere in the middle as a category. Some Realms are large in size, but contain many dead, dying, or dim worlds, as well as nebulae and celestial scars.
Micro-realms are small, both in size and components. They represent new Realms reborn from Oikumene, dying Realms, or artificially resuscitated or created ones.
Realms are as diverse in behavior and personality as any person. Most are asleep or sleepwalking - inhibited by the Immortality Dictum in the series. Like any other living, sentient being, they want to live, grown and find meaning in their existence.
Worlds
Within the Realms are a diverse list of different planets, moons, and other stellar objects. This list also contains conceptual and spiritual locations.
These are the worlds and include those otherwise given an intangible or indeterminate location, such as Huang Quan, Heavens Gate, Kabilao, etc., which are indicated as symbols in the Eschatos Diagram.
A world is defined as dead, dying, dim, or living.
Living worlds are exactly like they sound. They have life, howsoever defined, and a functioning Providence generating system. Living worlds are growing, in one way or another. Living worlds can be awake or asleep under the Immortality Dictum.
Dim worlds have an issue, either physically or have a broken Providence generating system. While not dying, Dim worlds rarely grow at any measurable or standard rate. Dim worlds can be awake or asleep under the Immortality Dictum.
Dying worlds have a broken Providence generating system and usually some kind of physical harm that is inhibiting them, such as the Sundered World or the Shattered Moons World. In the first case, the world was cut by the Sword of Immortal JuiyKu, which also lobotomized the world consciousness there. In the second, the beings that dwelled in the world broke their own moons, causing them to shatter and constantly rain down on the world. The same catastrophe killed the world consciousness, causing the world to begin to die off. Dying worlds can be awake or asleep under the Immortality Dictum.
Dead worlds are exactly that: usually barren, lifeless regions, like dead planets or irradiated zones of space. While dangerous, dead worlds are common sites of treasure hunting, mainly to harvest Realm Cores and similar treasures.