The Moon Lay is one of several overlay realms, which is sometimes referred to as the Lunar Lay. It is considered a sort of "in-between" realm, like a reflection. The Moon Lay can be accessed by creatures in the Material Lay through the usage of standing liths called Ghost Rings, which have the ability to concentrate moonlight enough to allow passage. Those who could do this were called Moontreaders. There are also creatures which exist in the plane, such as the wraighs. Likewise, it is possible to summon some to the Material Lay; those of the Tal Calar do this.
The Moon Lay was inadvertently created when the god Orend made the moon. As such, the moon gives of itself to this lay.
Magic in the Moon Lay
It should be noted that magic cannot be used inside the Moon Lay, and any creatures with magic within them could not be harmed within the Moon Lay, such as by wraighs or Eari Stones. One's physical body in the Material Lay could still succumb to the effects of the wraighs or Stones, which would trap them forever in the Moon Lay, making them Nightwraiths. Staying too long would also yield this same effect. Creatures in the Moon Lay can sometimes be seen and heard in the Material Plane when the moon is out, and cannot interact with ordinary physical objects. They can, however, use special objects that have been properly enchanted, such as weapons.
Transport
There are two ways in which to traverse inside the Moon Lay. Creatures not of the Lay, barring few exceptions, can only teleport to Ghost Ring sites, but regular movement is typical. Once inside the Moon Lay, treaders can transport themselves to any other Ghost Ring that has sufficient moonlight, however, they cannot return to the Material Lay as physical beings unless they regain their physical body (appearance in the physical plane simply means they can be seen by those in the physical plane; they essentially catch a glimpse into the Moon Lay, usually because there is ample moonlight).
Creatures that exist in the Moon Lay can instantly transport anywhere at any time, and some can transition to the Material Lay without Ghost Rings. They do this by using reflective surfaces as portals. This is how wraighs travel to their prey instantaneously. The Tal Calar are able to wield the Eari Stones through these doorways, and if the passage is large enough, can also pass through if so desired. The Stones give them the power to do so.