Magic

"Magic" comes in many forms. Most commonly it is recognized as one of two things. One, a source of energy or supernatural force that permeates the world and is often described as the "essence of creation", the essence of life, mana, chi, the force, or the soul. The second refers to the application of channeling that power to manipulate reality - also known as sorcery, the Art, wizardry, etc. Many supernatural beings are able to perform at least minor magic or naturally benefit from it through abilities or resistances they possess. Mortals that are able to harness magic go by several names, but the most common are: sorcerer, wizard, arcanist, cleric or priest, druid or shaman, and warlock.

Magic as a Supernatural Force

Magic is generated by the lives of living beings. Life-force itself is a form of magic including the soul and emotion. Living beings exude life energy as they live, a kind of natural magic that leaves a footprint of their lives on the world. This is why many powerful supernatural beings such as vampires cannot enter a home uninvited, because the life energy of a family living in a home - especially one passed from previous generations - has permeated the place in which they live so deeply that it will reject such an intruder stripping them of their magic and, in the case of some beings, destroying them on the spot. This phenomena is known as a Threshold. 
In most places the abundance of life from the smallest insect to the greatest beast blankets the planes with magical energy that sustains any spellcaster's ability to perform their art. The blanket of ambient magic is the same at all points meaning that spells do not deplete the magic of an area, but instead deplete the entire pool, like scooping a bucket of water from a well. However it is possible to isolate portions of a plane from that pool of energy, limiting the amount of magic available. This has been done to one place on Glan'Amar: The Dead Isles of Tol'Galen.
Magic exists in a multitude of forms from the barely detectable to the massively obvious. There are as many forms and uses of magic as there are colors in a spectrum, and for each profession that wields magic there are many sources they can gain it from. For instance, clerics gain their power from divinities such as gods or great spirits while wizards learn to channel and control the ambient magic in the world around them. More on this later.

Ley Lines

In addition to the universe-spanning blanket of energy, there are also currents of magical power that flow through a plane called Ley Lines. Ley Lines can fuel any practitioner's magic. A practitioner who harnesses the power of a ley line is capable of enhancing their skill. An experienced practitioner who does so is capable of overwhelming magic, but one must know how to use it in order to do so safely. Ley Lines are invisible to normal sight, but divination can reveal them as bright torrents of shifting colors of energy not unlike aurorae. They move through earth, air, and water unheeded, but tend to follow natural pathways such as rivers, mountains, and shores. They also tend to gravitate towards great centers of life such as cities or a powerful creature's lair. Wizards are sometimes known to build their towers in the vicinity of ley lines, and creatures such as dragons are naturally drawn toward lairing close to one as well. Ley lines are mostly harmless, but have been known to cause strange occurrences at times such as turning mundane materials into something more mystical (ie. Adamantite), causing areas of verdant or growth, or an area where stone becomes weightless. 
As ley lines follow natural contours, they do change with time. A city may fall or rise, an earthquake cause a river to dry or a mountain to fall and over several decades or centuries a ley line may migrate, but this kind of change is gradual and delicate, forcing such a change can be catastrophic

Magic as an Art

Magic harnessed to manipulate reality is known by several names and comes in several forms.

Wizardry

Also referred to as the Arcane, wizardry is the study of the metaphysical to the point of being able to manipulate it. Wizards are the most common users of this kind of magic, but artificers and some bards also employ it. This use of magic involves study and understanding of the universe and it's moving parts in order to manipulate them. Wizards often spend decades of their lives scouring over tomes and scrolls to learn how to harness their power. Though more difficult to master, it leads to more varied ability capable to adapt to several situations.

Death Curse

Wizards specifically, at the time of their death, are said to be capable of invoking what is known as a Death Curse where upon their death they release what power they have remaining and ultimately burn their remaining life-force away in order to strike a blow at a foe or foes. A Death Curse can be destructive and straight forward, or cruel and subtle depending on the wizard.

"Die Alone..." - A wizard's dying breath, and their death curse

Divine

Divine magic is possibly the most straight-forward of magic. A priest, paladin, cleric, or other receives power for their devotion to their god or oath from a godly being. This does not need to be a god, but a being of great power such as a god, devil prince, archdemon, or other being native to the universe. Divine casters call upon their gods with great skill and can entreat their aid with greater authority than other worshipers. There are few restrictions to a divine practitioner's ability to use their magic, but as they are granted power from their god rather than drawing it in from the world around them, if they are cut off from their god, it may dampen or sever their ability to cast or regain their magic.

Pacts

I put this here not because they fall under the same umbrella of magic, but because they ultimately act the same but with different sponsors of the magic used. Unlike divine magic, pact magic does not require a being native to the universe...

Soul

Sorcery is the most common form of soul magic, the most common (counting the entire universe) magic practiced. A sorcerer or other is born with the ability to harness the power of their soul to create magic. For most people this would be an exhausting if not fatal practice, but due to the supernatural nature of a sorcerer's bloodline their soul is able to recharge the energy expended quicker than others and using their soul as a source of power causes next to nothing in terms of side effects. Supernatural beings such as celestials, fey, dragons and fiends all use the same kind of magic.
Souls of other creatures can be used in other ways as well. Rather than using their own soul to cast magic, a practitioner can use the soul of another, often captured or drawn from the body it resides in, to fuel their magic. Doing this is often seen as an evil act (as it is often associated with devils and demons that do the same) but practitioners can and have used souls to enhance and empower their magic and have found it to be an extremely potent component.

Soulburn

A sorcerer or supernatural being is capable of casting beyond their perceived ability, but at a risk. Soulburn or Soulfire can be used to increase the power of their magic or to exceed their limits, but it takes a toll on their soul in the process and can cause serious difficulty up to and including destruction of the soul. It is often seen as a last ditch or desperate final act. 

Primal

Primal magic is primarily the magic of druids and rangers. Someone who uses primal magic is closely tied to some aspect of the natural world and therefore naturally draws power from their closeness with it. Sometimes this comes in the form of a great spirit of nature granting power or a fey or primordial spirit of the elements or simply the land itself. This magic relies heavily on the connection one keeps with the natural world and in turn with the universe at large. Many of these practitioners eventually learn to become one with the world in which they draw their power granting them long lives and different forms. The most important requirement for one of these casters is remaining true to the natural world so that it does not reject them.

Creation

The Song of Creation or the Music of Creation is a rarer form of magic used primarily by bards. Bards are able to learn how to listen to the song of creation that still echoes through the universe and draw power from it. This comes in the form of spells similar to the other forms of magic, but it also comes in the form of phrases known as Words of Power. Words of Power can be, if learned, used by anyone, but those with a skill for utilizing the power of the song of creation find them easier to use (ie. Bards). Many words of power have been discovered and lost by many different beings of power, but one of the most well known times when these words were used is during the Dragonsong War.

The Dragonsong War

The Dragonsong War was a plane-spanning war between dragons in the ancient past. While most of the evidence of the war has been covered, the histories from the time speak of the wars between the ancient dragons not as simple martial clashes, but as duels of voice and power that sounded like music weaving and clashing between the opposing sides.

Blood

Blood magic is used less often as a full source of magic and more as an enhancement. Blood drawn from a living being draws with it their life force which can be used to power spellcasting. However, this form of magic can be unstable and specific (Ie. spilling the blood of another unwilling, fearful creature won't enhance beneficial magic). Any practitioner can use blood magic, though it is a rare form of enhancement outside of certain religious rites.

The Dangers of Magic

Magic is an oft feared power, especially by those who don't understand it. But while those who use it should not fear it, it should be respected.

Spellwraith

Those who attempt to harness magic outside of their capabilities or beyond their power to control, if it does not simply kill them, can become a being known as a Spellwraith. Spellwraiths are beings of pure magical energy created when magic harnessed by a practitioner becomes unstable and begins to draw from them until the point that it burns them away leaving nothing but the chaotic magic that created it. Largely unknown, spellwraiths are dangerous and impulsive, capable of great magic, but possessing none of what made the practitioner themselves, believed to lack morality, compassion, or desire of any kind without it.

Type

Metaphysical, Supernatural