Aether, the Etherial plane

Each plane of existence is thinly veiled and connected by the Ethereal plane in which nothing was solid, including living creatures, their possessions, weapons, and armor. All metal became ethereal metal, flesh became ethereal flesh, stone ethereal stone, etc. The Ethereal touched every plane at all points and bound them to the other planes, but the connections were not abrupt transitions but rather a gradual process in what was called the Border Ethereal. If you consider the Ethereal to be an ocean, a person in the Border Ethereal would be standing in the surf near the shore, invisible to those on land but able to see them and their surroundings dimly.
By use of magic (or the natural ability that some creatures were thought to have, like phase spiders) one could fade into the Ethereal and travel at will. Gravity gave a sense of up and down, but movement in any direction was equally easy and objects released hovered in place.

Type

Plane of Existence