The world of the Seven Societies is intricate. It's what you'd expect from an extremely old group of arcane secret societies.

The below poem prefaces the text of the first draft  guidebook, Society; The World Behind the Veil.

Welcome to the rising,
so glad to meet you!
We have Daemons, dread Magi
Faerie and Aelf too

Knights and witty Psychics
Predict and defend
The Summoners well...
they know what they do at their end.

The Veil it is ripping
and we invite you to view
the madness of The Rising;
that's Apocalypse to you!

***

A few definitions:

'Sending/Sending: Short for 'mental sending'. A  sending is similar to telepathic communication. All Society members can communicate via sending, although some Paths fare better than others. A farsending is an extreme form of sending which reaches much farther than the usual sort. This ability is unifier between Society members across the globe. It transcends language and with a little help, distance.

The Network: Established before the beginning of common era, the Network allows mental sending to transcend distance. It works in a similar way to the internet. Psychics of the Third Society form node points for farsending between members of all Societies. Although convenient, this method of sending is prone to intrusion.

Pulse: A refined method of a brute psychological intimidation technique. Only Sixth Society Knights and Gladiators can pulse, although most other Societies can sense it. Partly because of this technique, Knight Weapons (particularly hidden ones) are built to respond to pulses.

Path: Each Society is built on six arcane Paths. Each Path is further broken down into two 'Treads/Halves'. In simple terms, there's two versions of each society. So far, three out of six Paths have come up: Psychic (Third Society), Faerie (First Society) and Knight (Sixth Society). More on these later.

QuickSilver: On of the basic Alchemycal Alloys (or TrueAlloys) quicksilver is halfway between liquid and solid. It has a corrosive reaction with dark essence, similar to its base metal - silver. Carlos' belt is actually a hidden weapon known as a whip blade.

Daemon: Within the underdark hierarchy, daemons stand at the top. They're more sentient than basic darklings, upon whom they can exert varying levels of control. Legion is a type of Mid-level daemon formed out a cluster of proto-daemons. 

Magi: (sin. Magus) The real equivalent of demigods, angels, warlocks and wizards from ancient human lore. Magi have the innate ability to twist reality in unpredictable ways. Their abilities are thought to center around intangible identities known as Talismans/Symbols. Talismans may arise spontaneously or be transferred from one bearer to another (like a virus), through murder. Barring extermination, Magi are also believed to be immortal.

Magi are named for the so-called "First Magus", Simon son of Antonius. Simon is more popularly known as Simon Magus. Independent and erratic, Magi are viewed as a threat by both The Societies and the Underdark.

The Underdark: The bad guys. More on them later