What are demons that are described in the bible? Where are their origins?

Demons are fallen angels.

Leviticus 17

Amplified Bible (AMP)

7So they shall no more offer their sacrifices to goatlike gods or demons or field spirits after which they have played the harlot. This shall be a statute forever to them throughout their generations.

Deuteronomy 32

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17They sacrificed to demons, not to God--to gods whom they knew not, to new gods lately come up, whom your fathers never knew or feared.

Psalm 106

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37Yes, they sacrificed their sons and their daughters to demons

Isaiah 13

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21But wild beasts of the desert will lie down there, and the people's houses will be full of dolefully howling creatures; and ostriches will dwell there, and wild goats [like demons] will dance there.

+++"Demons Demons are fallen angels under the command of Satan, those who are still free after the Gen. 6 affair. Satan is called the Prince, or Ruler, of all demons in Matthew 9:34; 12:24; Mark 3:22; Luke 11:15. Demons are also called the ministers, or ambassadors of Satan, Luke 4:35; 9:1,42; John 10:21. Satan is brilliant, an administrative genius. He has an excellent organization, mentioned in Eph. 6:10-12 (READ) The Bible also makes a distinction between demon possession and demon influence.

The so called "demons" in the bible are actuallly gods from Babylonian religions that they demonized by name just in an attempt to stop people from worshiping them so they would be forced into judaism and christianity. If you dont believe me just look up the demons names they mention.

There are no demons, why do you think there are? Because your holy scriptures mention them? The bible was written by ignorant men 2000 years ago and they did not have tv and the internet so they had huge imaginations.

That should tell you something about the NT then.

Before God created humans, he created a multitude of spirit creatures. These are the "sons of God" whom are referred to as rejoicing at the time when earths 'foundation was laid' (Job 38:6-7).

What should be noted here is that we humans of course have our own culture and civilization. It should not be strange if spirit creatures have their own as well, as they are intelligent creatures with their own free will. Of course we do not know much of anything about their culture or civilization but by the time earth's foundation was laid, the spirit creatures themselves had likely already existed for a very long time. Their civilization was therefore likely very advanced by our standards already then.

Just as we humans, spirit creatures can choose to use their free will to either obey or disobey God. Some of them made themselves to what we humans call "demons", by rebelling against what was appropriate for them according to God.

The demons are those spirit creatures that in the book of Jude (verses 6 and 7) are described as abandoning their own proper 'dwelling place'. The verses in Jude ties what the spirit creatures did with the immorality of Sodom and Gomorrah when it states:

"And the spirit creatures who did not keep their positions of authority but abandoned their own home-these he has kept in darkness, bound with everlasting chains for judgment on the great Day. In a similar way, Sodom and Gomorrah and the surrounding towns gave themselves up to sexual immorality and perversion."

The scriptures in 1 Peter 3:18-20 additionally ties the spirit creatures sin with the time period of Noah:

"For Christ died for sins once for all, the righteous for the unrighteous, to bring you to God. He was put to death in the body but made alive by the Spirit, through whom also he went and preached to the spirits in prison who disobeyed long ago when God waited patiently in the days of Noah while the ark was being built. In it only a few people, eight in all, were saved through water,"

And 2 Peter 2:4-6 also talks about the spirit creatures sin as follows:

"For if God did not spare spirit creatures when they sinned, but sent them to hell, putting them into gloomy dungeons to be held for judgment; if he did not spare the ancient world when he brought the flood on its ungodly people, but protected Noah, a preacher of righteousness, and seven others; if he condemned the cities of Sodom and Gomorrah by burning them to ashes, and made them an example of what is going to happen to the ungodly;"

So from above verses we can see that the sin that the spirit creatures committed was of sexual nature and happened at the time of Noah.

The sin that the spirit creatures committed is described as follows in Genesis chapter 6, verses 1-4:

"When men began to increase in number on the earth and daughters were born to them, the sons of God saw that the daughters of men were beautiful, and they married any of them they chose. Then the Lord said, "My Spirit will not contend with man forever, for he is mortal; his days will be a hundred and twenty years." The Nephilim were on the earth in those days-and also afterward-when the sons of God went to the daughters of men and had children by them. They were the heroes of old, men of renown."

One could then ask, how did the spirit creatures have sex when they are by nature immaterial?

In my opinion this must have involved a transfer of the spirit person's mind to a separate physical body, similar to what humans were portrayed as doing in the "Avatar" movie. I think that with sufficiently advanced technology something like this would well be possible.

As was explained above, spirit creatures had likely existed a very long time already by the time earth was created, and as a consequence likely have a civilization with a high level of what we would call "technology" (likely not exactly applicable in the same manner in the spirit realm, however).

The spirit creatures "materialized" in the sense that they took over human-like bodies in order to be able to enjoy sexual relations with human women. I say "human-like" because their offspring is termed in Bible "nephilim", which indicates that the offspring may have not exactly been human and thus one of the parents was not exactly human. The situation eventually developed into a point where God saw no other solution but to wipe that world out of existence.

The subsequent flood destroyed the humans outside of the ark and the hybrid nephilim, and forced their fathers back to the spirit world, where they were no longer allowed to be part of Gods organization. They thus became part of Satans organization of rebels. Although they are seemingly no longer able, or allowed, to "materialize", they do like to take over human and animal bodies in what is called "possession", likely because of some enjoyment they infer from this.

The source articles have some more info about the demons.

they are fallen angels.