Demon is the term used to refer to any of Hell's inhabitants.
Demons are long lived creatures that preserve their long lives and power by repeatedly resting for periods of a hundred years every several hundred years. Stronger demons sleep for longer periods of time. As demons only need Sleep, it's possible for them to live forever. 
Demons have multiple souls. 
A demon increases their standing by killing, and/or taking the souls and power of other, greater demons.
A demon can make a contract with a human, which would make the human a demon upon their death and a member of the Family or Household of the demon they were contracted to.
Fallen Angels/Pure DemonsEdit
The terms Fallen Angel and Pure Demon are not synonymous.
Pure Demons are, along with Fallen Angels, also Gods of other Worlds that were swallowed up by this one ("The World will become One, when God becomes one") that have Fallen to Hell in order to avoid "Disappearing" (dying).
Pure Demons are thought of as stronger than Nephilim, and most hold disdain for the latter.
Nephilim are demons that used to be human, but made a contract with a demon and came to Hell after their deaths.
Nephilim often have marks that distinguish them from Pure demons. Dantalion has one on his neck, Astaroth one on her stomach, Gilles de Rais has one by his left eye, John Dee has a marking of a third eye on his forehead.
There are individuals who are only a demon by half, but are still considered demons.
A demon can have a Household or Family.
A bond between household members is like a contract. Members don't have to be related by blood, or even the same race, but by the contract they can give each other power in exchange for never betraying one another. By dividing power demons share the same consciousness, and memories.
A household is like a relationship between master and servant, like a contractual agreement, like the relationship of a Family, like the relationship between lovers. But every household is different. John Dee comments that if he were to say it in a single sentence, it's stronger than the bond of blood - in a sense, it becomes their greatest weakness.
Once someone becomes part of a demon's Household, they can protect that demon's territory and property. It's possible that they can even inherit that demon's title. There are many demons willing to become part of a Household.
In the old days, there were four ways a Demon selected a household member: first - they looked for the one who's life had run out (John Dee), second - one with a desire for power (Gilles de Rais), third - one with an intense hatred, and lasty - one who is fascinated with this world.
The one to whom the Household belongs to would have to impart power on a household member.
It can be more than a contract, and if one person is weak then the other can give them power.
- ↑ Pillar 57, pg 19
- ↑ Pillar 57, pg 3
- ↑ Pillar 55, pg 17
- ↑ Pillar 72, Cassandra
- ↑ For Reference: Samael is a Fallen Angel (and Pure Demon), Baalberith was a God that acquired the rank of Angel and Fell - so is a Fallen Angel (and Pure Demon), Pluto was a God once that descended to Hell - so is a Pure Demon (but not Fallen Angel)
- ↑ Pillar 25, pg 27
- ↑ Pillar 58 pg 5
- ↑ Pillar 58, pg 18,19
- ↑ Pillar 51
- ↑ Pillar 52
- ↑ Pillar 54.5 pg 15,16
- ↑ Pillar 54.5, pg 10
- ↑ Pillar 59, pg 8