The Ethereal Plane

The Ethereal Plane, also known as The Border Ethereal or simply The Border, is one of the eight planes of existence that make up the Great Prism cosmology. The Ethereal Plane is a transitional space, a "plane between planes"that links the other seven planes together and facilitates travel between them via the Convergence Zones.  

Characteristics

The Ethereal Plane has no defined characteristics of its own; instead, the plane is an empty space which serves as a barrier between the other seven planes; a visitor to the Ethereal Plane would find themselves seemingly still within the same plane they departed from, albeit completely invisible and intangible to the world itself.   Certain spells exist that, if successfully performed, allow a magic user to freely travel to the Ethereal Plane; likewise, any creature with the truesight ability is able to view entities within the Ethereal Plane, though it would still need to be on the plane itself in order to interact with them.   Convergence Zones between the planes exist in areas where the barrier created by the Ethereal Plane is thinner than usual; this can occur for a variety of reasons, though usually as a result of a high concentration of magic within the area. While most Convergence Zones are naturally occurring, it is believed that the ability to create artificial doorways between the planes was once a highly-prized ability of the elves; in the Modern Era, there appear to be no surviving elves capable of performing such a feat of magic.  

Inhabitants

As an empty void, the Ethereal Plane has no native inhabitants, although a variety of creatures are capable of accessing the plane: some predatory monsters, such as the terrifying Phase Spider, are able to shift into the Ethereal Plane freely and incorporate this ability into their hunting strategy. In other cases, incorporeal undead such as ghosts, banshees and wights are believed to be the spirits of the deceased that, for one reason or another, were unable or unwilling to depart from the Prime Material Plane to the Shadowfell.