Ladies and gentlemen, it is with great pleasure that I present to you my latest partial attempt at formulating a Universally Accepted Model (tm) for the non-physical universe. I'll be honest with you, this is what makes the most sense in my mind after reading about a million and a half books on the subject, but that doesn't necessarily mean that it's accurate or "true." Oh yeah, and I hope it'll make sense, 'cause it's late at night and I'm just not that good at explaining
Here's a diagram:
At the root, we are a blob of timeless, formless, sizeless thought energy that we like to call "the higher self". Inside this blob, we as persons are a subset of this thought energy. We are a sub-blob that contains our thoughts, our memory, everything that defines our identity. Within this sub-blob are all of our different focuses of consciousness, including waking consciousness.
Now, thought energy is vibrating, intangible, inexistant "stuff" that carries data. A memory of the word "tree" is an encoded blob of thought energy inside our consciousness that carries links to other blobs of thought energy that define it. The defining blobs could be things like memories created by a being after seeing a tree, memories created by a being after reading the definition for "tree" in the dictionary, all the expectations of what a tree should be in that person's mind, etc. Thought forms within a person's "blob" are all interconnected in some way. When you have a loss of memory, you actually have lost the link to the memories you were trying to access, but the memories are still there, intact, as thoughtforms, somewhere inside your "blob." Through altered states, it is possible to look beyond the confines of physical memory and retrieve lost memories from the blob.
The environment these giant blobs of thought energy we call higher selves are located in, that's what we call The Astral Plane.
An Astral Realm is a set of interconnected thoughtforms within one of these blobs.
I took Astral Pulse Island as an example in the diagram. Adrian, who is a subset of his higher self, and a subset of All There Is, one day decided to create a subjective Astral Realm that he named Astral Pulse Island, within his own consciousness. In this case, it was very much a "Dreamscape" ; a fictional place that existed only in his mind. The thoughtforms inside this Realm are an island, a pyramid, water, the sky, palm trees, etc. Adrian then gave other people the directions to this Astral Realm so they could visit it.
When a person decides to visit Astral Pulse Island, all they have to do is locate Adrian's creation, stretch their blobby appendages and connect with it.
In much the same way, our physical universe is an Astral Realm within what we like to call The Creator. The Creator owns all atoms, particles, our physical bodies, the emptiness between atoms, etc. The creator was particularly clever in that his Astral Realm is not made of concepts. Each atom is actually made of persistent little heart-shaped balls of energy. We are not our physical bodies, we are a blob in another dimension that is remote controlling a physical body, you dig? What we really are in this plane is an etheric body, a blob of energy that is capable of sending energetic impulses into physical matter. The etheric body is responsible for the exchange of information between the physical body and the mind. In energy work, telekinesis, "soul healing," we learn to direct energy outside of just the brain in order to alter physical reality.
The Astral Plane is a large mass of thought energy containing many fragmented subsets that like to call themselves identities. Each subset has an infinite size and can contain many interconnected thoughtforms. Your own mind, I'm sure, contains many worlds of your creation.
So when you visit the Astral Plane, what you are visiting is a subset of your consciousness. You may decide to visit or suddenly find yourself in an Astral Realm that was not created by you. This is extremely rare, usually there is a reason behind it. What happens is that you make your own personal blob, your consciousness, intersect with another entity's consciousness and access a set of thoughtforms. That realm may be as tangible as the physical world, especially if it was created by a human being. It could also be "weak" and be shaped mostly by your mind if the entity that created it did not put much energy into making it stable, or if it has nothing to do with physical consciousness.
Let's say you find yourself in an Astral Realm where all the beings are red balls that talk to each other solely using muscal tones. You may very well see them as people having conversations. They'll see you as a big red ball that has an unusual way of beeping 440 Hz to say hello, and neither party will know how different they are from each other!
The Astral Plane is all about how you use your thoughtforms to relate and connect to other thoughtforms in the universe. The Astral Projection experience is in many aspects like a dream, because a plain old dream also happens to be a weird thought form salad.
Anyway, I'm off to detach my blob from my physical body and intersect with other parts of All There Is. See ya.