Defining Demons/Deamons is a very difficult subject. The concept of demons is very old, and transends many cultures. Egyptians, Zorastrians, and most ancient religions and civilizations had some sort of concept which coresponded in some way to the modern idea of deamons.
The Greek word which would most closely respond to the word Deamon, isn't necessarily negative in conotation at all. It means a god or goddess, or any other entity higher than man, and lower than God. It also means THE divine power... so technically the ancient word Deamon isn't necessarily a negative thing. However in common usage it has become so. Its origion... also has a bit of negativity in it. It may derive from a word indicating to divide, or to distribute. There in may be the true problem with demons... they divide... as opposed to unifying. On the other hand the ancient usage of the Greek word also indicates the higher self, or the spirit of a person... thus the Greek Deamon isn't really what people mean when they say Demon.
The ancient hebrews believed in pleasant and unpleasant demons. They believed in both the se'irim and the shedim. The former was a sort of Satyr type being, or faun... which had no negative connotation at all really, just that they like many other cultures had seen them. Some very early jews offered sacrifices to them, but other than that... there was no negative sense to their belief in them at all. Shedim on the other hand were seen as more sinister, but part of a sort of negative aspect of Kaballistic practice... where one could make a golem. That word was also used for idol worship, and possessing and troubling entities... and that is very akin to the usage we all tend to think of.
Overall the concept that Daemons come in two categories, harmful and benign is echoed in Hinduism, Zorastrianism, and many many other religions and cultures.
Myth wise, Bad Daemons do things like eat your soul, or possess you and cause you to kill your children. They inhabit idols, and demand sacrifices, where as Good Daemons help you, or at worst ignore you and frolic in the fields like fauns.
Much of the bad press which these Demons/Deamons get is from the Christian Faith, and of course the modern cenima. It is clear that the bible complains of Bad Demons, but doesn't mention the good ones as any relation to the bad ones very often at all, but there are references to Angels, and heavenly beings called elders, and also the creatures with four faces, and many somewhat disguised female entities etc. Thus the Bible makes its own distinction between good and bad Daemons, it is just specific in the type of creature it means... so that the name is specific in the connotation.
The most common words for the negative Demons in the bible are as follows.
Satan
Belzbub
Devil
Spirit
Evil Spirit
Unclean spirit
Satan just means Adversary, litterally one who resists, opposes, or withstands. It could apply to any opposition to God, or God's people, though generally Satan is thought to be Lucifer, it is more correctly assumed that they mean Belzbub, and the Gnostic texts leave little doubt that at least part of the time when Christ says Satan he means Demurge.
Belzbub - variously translated Lord of the Flies, and Lord of the house... he is known as the prince of demons. He likely corresponds to the entity Bael, whose followers sacrificed their own children to him, by burning them alive. Not really a nice guy.
Devil - diabolos occurs only in the new testiment. IT means slanderer, or false accuser. That preticular word isn't always used to indicate a Daemon at all... it can mean a human person. It doesn't denote power or lack of it, only the action of falsely accusing. All of the occurances of the word Daemon are also translated devil also... so that makes the KJV confusing. In any case diabolos in the negative sense used in the Greek means a guilt causing spirit, or a spirit that makes you accuse others. A demon that makes you do wrong and then points the finger at you... which is kind of a cruel trick. Most of the time in the bible Devil is used to denote a possessing entity... about to be cast out, so the inference is that this creature makes people do wrong, and then makes them feel even more guilty... thus they need to be gotten out of the person.
Spirit - pneuma has both amazingly positive connotations, and deeply negative connotations... depending on the entity. It means litterally a movement of air. I think I'll just quote Strongs Concordance site on this one. They explain it pretty well. I'd like to add though that it basically means the breath of God, breathed into each of us... that is why the connection between God, daemon and man in this word. It is the one thing we all have in common... and is good or bad depending on personal choice.
www.blueletterbible.org/cgi-bin/words.pl?strongs=4151Unclean spirit - a spirit which has been corrupted or contaminated.
Evil Spirit - It is funny considering so much has been made of the belief in good and evil, but the original hebrew root of this word means to make a loud noise. There are two Greek words used, one is Ponos which means pain, trouble and intense desire. The other word is penes, which means to toil in poverty for daily sustanance, and still be in dire need. Thus we see that Evil simply means suffering, or something that causes it. Evil spirits are something that make us suffer, live in poverty, and pain, and cause us trouble.
Thus was the reason for exorcism, not to cast out Daemons, but to remove spirits that were contaminates to the human spirit. Spirits that lead people to work against their own best interests, and make life difficult. When we see a man working hard, and still living in poverty because of some curse like problem then we know that it is compassionate to solve that problem for him.
Most of these low level spirits are no more than negative energy that builds in a person's aura, until it forms an entity, then these entities. work against them.
Most all New testiment accusations towards Demons, and spirits are directed towards possessing entities, in the instruction of exorcism, not of Daemons in the propper Greek usage, but towards evil and contaminating spirits that hurt people. Thus the apparent connotation of evil. There are many spirits, deamons, and entities which do not possess, or plague humans. I have worked for many years in the field of Deliverance, and inner healing, which is in essence exorcism, and I can tell you that most all cases involved low level spirits, who were very little more than moods. Moods so powerful due to repitition, and traveling back and forth between persons, that they became entities, because they were fed human breath and life... the God force within us, which has the ability to create.
People subconsciously create evil spirits, and because they are created with God's creative power through us, they often live for hundereds of years, going from host to host spreading some miserable emotion, and the self defeating practices that go with that feeling. That is why, in the bible it speaks of certain "sins" causing a person to be cursed to the seventh generation. It is not that God directly causes a curse to be placed on a sinner that effects their great grand children. It is that the energy of that emotional malfunction, which caused them to do that, travels around in the family, and can survive up to seven generations, going from parent, to child to grand child. These things can be broken though, so that we do not have to suffer our great grandparent's moods for all our lives. In addition these things transfer to friends, lovers, and other people we know, if they are of like mood. They build in strength over time, and the more people feed them the stronger they get.
Thus most, but not all possession is by these "spirits." Occasionally something else negative will possess a person, but generally people suffer most under oppression by these humanly created spirits.
As for Daemons... I suppose we are all Daemons and in our higher selves, but we must remember the only negative connotation of that word is Division. In being proud of our higher selves, and obedient to our immediate superiors in the chain of command in whatever world we live, we have to remember that there is a central force. Something that ties us all together, that breath of life. The oneness of the universe, is challenged by too much belief in Daemons, at the expense of seeing the big picture. It is well to see the various gods, and godesses, but we must also see that it all works together in a sort of pattern. If we don't try to keep sight of that, we get out of balance. We all do what we do as individuals, but we also feed on the same cosmic energy, which is the pure universal energy of all of us, and the universe.
We are also all spirit as well as flesh, and as such we are all spirits, capable of being clean or unclean. We can flush out contaminates that seek to wreck our lives, and purify our energy through energy work. We all wrestle with our inner demons... but not necessarily Daemons, more like our own feelings, and those contageous feelings of others.
I suppose though that you may be wondering about Fallens, and princes of hell etc. All I have to say about them at the moment is that everything is part of God. We are all part of that same breath, angel and fallen alike, but some of us chose to be adversary. It isn't a one time decision. Every day we each choose, to be part of the problem or part of the solution. We decide whether to flow in unity with the universe, or stand in opposition. At times it doesn't seem that clear cut though, and due to the fact that the adversaries, are numerous, and not all on one side, unified together, but rather sometimes in opposition to each other as well, it is hard to know at times exactly what is "evil" It seems to have a lot of colors, shapes, sizes and flavors... but in general evil causes suffering. Anything that doesn't either by intention, or result cause suffering, isn't evil. Anything no matter how holy it presents itself to be, which brings about suffering, for no reason, without end in sight, and forces people to live in it and persecutes them endlessly... is evil. Thus historically most governments, churches, families, people in general, have been "evil" at one time or another, because of influence by these things.
I know I get preachy in spots, but I think it needs to be said that in speaking of Demons, we don't just point the finger out there, to some distant hell place. WE are all influenced, and daily we decide what we are influenced by. We all influence others, and our moods determine how we influence them. We decide to make life easier or harder on ourselves and others. We decide to be adversary, or accomplice, to all kinds of things, which are good and bad. In short the only difference between and angel and a demon is intent.
Kim