Astral Plane

The simplest definition of a plane, is a level of existence. Each plane has it own rules and if an entity want to exist in a particular plane the entity must respect the rules of the plane . As humans, we reside in the physical plane at least this is where our consciousness is focused, we are multi-dimensional being, we have part of ourselves in different planes but for our survival in the physical plane, our conscious simply ignore the other existences for example as you read this, you think of yourself as a man composed of blood and flesh or as a soul expressed into an human body. 

The physical plane is generated by its inhabitant, the humans create their experiences with their emotions, feelings and beliefs. Many thing are specific to the physical plane other plane follow other rules, there is no two planes similar, astral travelers know at least two planes the astral plane and the physical plane, the astral plane is much more like an extension of the physical plane a transition place or doorway to access other planes. 

Some planes don't have particles, therefore an entity composed of particle cannot existence there unless this entity learn how to transcend itself to make the transition, some planes don't have polarity good/bad above/below, to explore such plane an entity be it a man must transcend itself to the point, he can navigate and understand this.Therefore using this a person can navigate to a different plane which is quite similar to our own.This phenomenon is generally referred to as OBE (Outer Body Experience) although it requires in-depth knowledge about the different methods in which we can transcend to a form by which we can materialize into this plane