This is a really interesting explanation from the following site, which has given me much food for thought: http://www.rickrichards.com/astral/Astral11.html
Artificial Astral Entities are the creation of human minds by way of concentrated thought-forms. They are created unconsciously by persons who manifest strong desire-force with definite mental pictures of that which they desire.
They are not really entities in the strict sense of the word because they have no life or vitality, except that which they borrow from or are given to by their creators. Strong wishes/desires/mental pictures (whether good or bad) can and will eventually manifest in form with a semblance of vitality in shape of these artificial entities.
These entities are under the law of thought-attraction, meaning, they go where they are attracted. They can also be neutralized and even destroyed by positive thought properly directed.
There are other Artificial Astral Entities (thought-forms) whose creator creates them unconsciously. For example, a strong religious mother prays for the safety and protection of her children. Her imagination pictures "heavenly angels" by their side.
Unbeknownst to her, what she has created are "thought-forms" of angel guardians around her children; guardian angel(s) who were given a degree of life and mind vibrations from the soul of the mother.
The guardian angel(s) serve to protect and warn her children from danger, evil, temptation, etc.
"Thought-forms" can sustain their existence for a long time, even for generations (ie. historical ghosts walking the halls of old castles on certain anniversaries, or haunted houses where ghosts may be "laid" by anyone familiar with the laws of thought-forms.)
It must be remembered, these "thought-forms" are purely human creations and obtain all their energy (form/shape, mind and action) from their creators. And repeated thought, and repeated belief will serve to keep alive and to strengthen these entities, otherwise they will disappear in time.
THINK ABOUT THIS: Supernatural visitors, saints, religious figures, minor gods of the Orient, semi-divine gods, and even the appearance of the Devil and his evil work (witchcraft, diabolical personages, etc.) have been created/formed by "thought-forms," and in many cases, kept alive by the "faith" of the devotees of the church, chapel or shrine.
Other phenomena that belong to this group include, the effects of sorcery, black magic, voodoo, charms and even "spirits," which sometimes appear at spiritualistic seances. They all arise from this principle of "thought-forms." They are not human beings at all.
An understanding of this "thought-form" creation principle will aid in the interpretation of many puzzling phases of psychic phenomena that is observed today.