Chaos is the universal and usually malevolent metaphysical force embodied by the intelligent entities comprised of pure magical energy that live in the Realm of Chaos.
The entities who embody Chaos are mostly Daemons, but the term also encompasses those mortals of many intelligent races who have thrown in their lot with Chaos and form the so-called Grand Alliance of Chaos, often more simply referred to as the "forces of Chaos."
The term "Chaos" is also synonymous with the turbulent magical or empyric energy that gives shape to the nightmare domains of the individual Chaos Gods that are collectively called the "Realm of Chaos" by scholars of the Mortal Realms.
Chaos is a great and raw force of change and power, and is both physically and spiritually corrupting, though it is not in itself necessarily "evil."
While its adherents and servants act in ways that are often malevolent, some devotees of Chaos are more dedicated to the service of freedom and change than of the pure selfishness that Men and most other intelligent species define as nefarious.
However, more often than not, the Chaos Gods reward individual accomplishment in such a way that the ends justify the means, and the absence of hierarchy and emphasis on individual freedom leads to the pursuit of excess and personal aggrandisement that can only be characterised as damnation.
Mages can utilise and shape Chaos energy, which laymen refer to as "magic," thus making them capable of abilities which transcend the standard physical laws of the Mortal Realms as Men, Aelves and Duardin understand them. However, the malevolent power of Chaos can gradually corrupt a mage, tainting their mind and body and turning them into the slave of the Ruinous Powers.
The most powerful entities of Chaos are the five great Chaos Gods, also known as the Ruinous Powers, who each embody one aspect of the greater force of Chaos and can be worshipped individually or as an entire pantheon known as "Chaos Undivided."
The iconic symbol of Chaos is the eight-pointed star, representing the infinite possibilities of Chaos. Ultimately, Chaos and its entities seek nothing less than the complete destruction of the Mortal Realms just as they once did the World That Was, so that all of Creation is consumed yet again by the primordial and uncontained energies of Chaos.
In general, Chaos is a malevolent spiritual force that represents the collective negative aspects of the psyches of every sentient being in the Mortal Realms, and most likely in the wider cosmos.
Because Humanity is by far the most populous intelligent race of the Mortal Realms, the Chaos Gods particularly embody Men's myriad and particular flaws as a people.
Chaos corrupts Mankind so easily because it speaks to the character flaws inherent in every man and woman and seeks to exploit the weaknesses of their all-too-Human natures. It takes an extraordinary individual of truly iron will and selflessness to resist the serial temptations of Chaos.
It is also these inherent character flaws that produce the rampant physical and anatomical mutations of individuals exposed to Chaos energies, as these mutations are driven by the inner flaws of the person's psyche being made manifest in their physical person as Chaos bridges the gap between the pure magical energy of the Realm of Chaos and the realmspheres of the Mortal Realms.
With all the obvious dangers associated with Chaos, such as mutation, daemonic possession, and spiritual damnation, some might wonder why anyone would willingly choose to serve the Ruinous Powers. The answer is actually simple.
Chaos judges its servants solely on their abilities and their records of success and failure in promoting the agenda of the individual Chaos Gods and of Chaos as a whole.
Chaos also offers those who serve it the opportunity to perhaps one day wield power and respect far beyond the dreams of most mortals' avarice. For so many people, but particularly in the feudal realms that dominated the Mortal Realms throughout the Age of Myth and later, too often family connections and inherited wealth are rewarded rather than ability.
Where it is impossible in many realms for a talented individual to ever better their lot, Chaos actually offers a substantial degree of freedom and the only real meritocracy that they have ever known.
But Chaos is not a benevolent force, and for the vast majority of those who fall to Chaos' temptations, they will never reach either power or position and will be little more than faceless puppets in the endless schemes of the Dark Gods.
While Chaos may reward success with power, even the mightiest Chaos servant becomes a slave of Chaos, never its master. Most who serve Chaos will fail in their quests for power, eventually ending up as a possessed host to a Daemon, a mindless Chaos Spawn, or simply as just another corpse in the heap, a pawn whose usefulness to the Ruinous Powers has ended.