What they are: Entire, distinct world planes.

Their Mechanics: They are fundamentally flat worlds where standard visual perspective (as human eyes see it or as drawn in 3D perspective) does not exist. The sizes of objects and entities are governed by entirely different laws of physics.

Perception Rules: Beings living here have a direct, forward-facing gaze, yet possess 360-degree ambient awareness. They perceive things existing behind them simply by choosing to direct their focus toward them.

What they are: The individual "lines" or structural micro-layers within a single sub-dimension.

Movement: As beings travel, they move along a single stratum. They can also pass rapidly through many strata without noticing—unless they deliberately choose to focus on the movement or possess the innate ability to do so.

The "In-Between": When moving through strata, a traveler can become caught in an in-between state, which allows them to transition or phase across into a completely different sub-dimension.

What they are: The overall macro-structure that encompasses everything.

Scope: "Layers" is the overarching concept that includes all sub-dimensions, the in-between spaces, and the individual strata within them.