The Nature of Magic

Magic is an inherent part of our lives. And something we have discovered with newcomers and transplants is that the ability to do magic is not at all related to descent here. It is something apparently inborn in every individual, but since Earth does not have magic it only ever comes out when the individual comes here.
With that being said, it is important now to make a distinction between magic—inborn and instinctive to all of the sentient beings of this world, but something that must be grown and practiced and nurtured to be any good—and natural abilities, which are created and designed and thus something distinct from magic. Such things as setting something on fire with one’s mind are natural abilities, if it is performed without use of a spell or ritual or some other form of practice.
These abilities can be granted via magical ritual, or large amounts of esoteric radiation, or genetic modification, or excessive implants, etc. As you can see, there are myriad ways to gain them. They are usually limited in scope and only a few can be applied to one person, so they must be chosen carefully.
Usually the procedures for gaining these abilities are painful and difficult, so not many people are willing to undergo them. Most heroes have at least one. For overlords, the numbers are about fifty percent. On one hand, useful abilities and increased ability to impress and control one’s troops. On the other, the risk of the procedure and of depending on a fallible ability that might give out at exactly the wrong moment.

Spellcasting

In their most basic form, there are two dynamics to magic: the physical and the inscribed. The physical portion relates to inborn magical power, potions and formulas, enchanted weapons, and even the clothes the magician wears. The inscribed refers to that which is spoken, thought, or written in order to give shape to some piece of magic. When being technical, only the inscribed is spellcasting, but the word can also be used to define magic in general.
The physics behind spellcasting is beyond my knowledge. I know there are in fact scientific reasons behind why they work, but I could not possible tell you, the reader. I know proximity to the thing the spell is being cast upon is absolutely essential. I know the precision with which the spell is made is important, and I know the form with which it is cast deeply effects the potency and varies from spell to spell. Most of them need specific conditions, and some require physical components such as ingredients or specific items or certain energies in place.
Spells are short phrases or even single words that can be used to do quick work. They are recorded on paper and passed on from generation to generation. One of the more famous, or perhaps infamous, tomes of magic is the Graviloxicon, a gravity-powered magical book about, among other things, salty salmon. The most popular spell is “I can’t believe it’s not Fish People,” a lower cost alternative to the usual Fish People spell.
There are certain varieties of spells that require specialists with years of training, like permanent concealment spells for things like castles. These specialists can, therefore, require vast sums to perform their task, but a side-effect of the training is that they usually turn into eccentrics or outright go insane, so their fees can be unusual.
Rituals and invocations are somewhat akin to spells, but not precisely the same. By the way, invocations have nothing to do with pagan gods or demonic powers. As far as I understand it, an invocation is a specific type of magic that creates an object. This can be a temporary or a permanent effect.
Rituals are the long form of spells, and are distinguished by the fact that there is always a physical component and they always happen in stages. Spells can be safely combined in any order without any negative effects (at least, not related to the casting itself). Rituals are specific processes that must be performed in order and in such a way that is unwise to attempt two at once. Enchanting is a subset of spells that give certain effects to objects. Runes are a slight overlap between the physical disciplines and the inscribed disciplines that requires a specific setting and specially enchanted ink as well as a set way of writing or creating them. If that makes any sense.
Ley lines do come into it. The natural magic of the world can afford wizards of average quality a bit more power, and ley lines greatly assist in transportation spells, particularly long distance ones. Relying on them, however, can cause some disruption since if another magician uses the same ley line, one or both of them might be thrown off whatever they were trying to do.

Deormic Magic

Not technically different magic, but applied in a way that is distinct from most other styles. While most other magic users in the world will use some combination of words, books, objects, songs, hand gestures, etc., the mages of Deorma almost exclusively use magical energy from their surroundings to fuel them. This means that they're not always effective, since there isn't always enough magic for the purpose they have in mind.
It does, however, mean that there is a lower barrier to entry in terms of education. It's a more inherent skill, an instinct that one either possesses or doesn't. It's a lot more subtle in function as well, fueling existing actions rather than causing spectacular displays. Mostly. (See Blaze of Glory for instances otherwise.)

To Summarize

Natural abilities: Something that only a select few individuals possess; something that is highly specific to a particular element; something that is gained through specific sets of circumstances; something that is activated instinctively, without training or particular strain.
For example, someone who can now breathe ice thanks to an accident in a tundra laboratory.
Magic: A source of power that everyone has, albeit to varying degrees; something that is non-specific in its application; something that is trained up to be more effective; something that must be used with the aid of either extreme mental focus, spell words, arcane devices, rituals, etc.
For example, someone who uses a staff and a selection of Pragallic words to do anything from defrost a windshield to growing flowers in the garden, and who without the staff has great difficulty in doing any of those things.

Type

Metaphysical, Arcane