Ok...... here's the deal: <br />
Satan's former name is Lucifer. Lucifer is the "Fallen Angel" mentioned in the Bible. Demons are those "angels" that" Lucifer" took with him after he was cast out of Heaven.<br />
Satan is refered to by many names including, but not limited to: The Devil, The Dragon, The Serpent, Beelzebub, The prince of the power of the air and more.<br />
The Devil and demons are not the same thing. "The Devil" was an "Archangel" who became jealous of God and was punished by being cast out of Heaven. Upon being cast out, "The Devil" was allowed to take many angels with him and upon those angels being cast out with The Devil they became "demons".<br />
To keep it as simple as posible: The Devil is the "ring leader" and the "demons" are his "lackies".
The following is my understanding of it:<br />
"The Devil", "Satan" I understand are creations by humankind - thought-forms - on which to blame their transgressions; and because so many people believe in them, they are invested with a lot of power. That power is sourced from all the life-energy that people put into their belief. These beings - as far as I know - do not have an independant existance. That is, if EVERYONE stopped believing in them, they would dissolve as the energy given to them ran out.<br />
The concept of "Demon" is a bit more complicated.<br />
I believe that until a few years ago, when some changes were made to the inner dimensional worlds, there were (for example) human beings who died in circumstances where they had a very strong thought / feeling of hate towards something or someone; and they carried that mind-set over into the "astral" world, and henceforth were bent upon getting revenge, which they thought was their due. There were other demons who liked to just scare humans - as the terrified energies emitted from such humans was like food to these demons. So they went around on the dimension just above us in the physical, putting humans who were aware of them into scary situations, to feed off their vibes.<br />
A few years ago now, the Lower Astral worlds were purged and cleared of such beings.<br />
However, there's another class of malevolent beings that I know of, which are still around, and do mess with humans a lot. They are the several types of so-called "Reptilians". They are quite often the instigators of crimes of violence, by mentoring susceptible humans through mind-power. Its a bit like that idea of a devil on the left shoulder telling you to do so and so, while your Angel on your right shoulder tells you to do such and such.<br />
"Susceptible humans" are those who have karma of various kinds, which the Reps. are able to play upon and magnify; and these humans are also people who are not protected by proper grounding to the Earth.<br />
Another class of "demons" are parts of one's own personality which have originated from within the unconscious mind and have reflected outward into your own outer experience, to tell you that they're there, and you have the opportunity to work to change their nature and integrate them into your being, so that they are no longer causing a disturbance. If you know how to do that... and recognise what's going on.
the devil (lucifer) was an arc angel and basically is the boss of bad (only 1), A demon is a servant of the devil, one of it's footsoldiers or servants.
the last three letters
its between you and me ... wahahaha
the demon is the devils worker.