Magicka Energy

The natural energy of the Arcane Triad - a lesser form of the power of pure creation weilded by the deities. 
It is said the deities of the Arcane Realms wished for their peoples to know the same joy of creation they had experienced - and so they blessed their peoples, the elves, fae, and dragons, with the ability to manipulate energy as they did. 
However, pure celestial energy is too much for any mortal to handle - so the deities tempered it for their peoples, allowing them only limited powers in comparison to theirs. 

Magical Affinities

Like the deities have domains, mortals have affinities - in the early days of creation, these affinities were strongly tied to the patron deity of a people. This was because the deity could only grant powers to others they had themselves - but over time, mortals came to be born with affinities not tied to the patron deities of their people. Some of this was due to the way mortals naturally travel and intermingle, and some due to the celestial spark that gives mortals free will and being composed of mutliple elements allowing them to break from rules that bound their deities. 
This is also perhaps why affinities defy easy categorization - while there are broad categories that most affinities fall under, there are also extremely specific forms of magic used only by a few. Often, these are categorized as subtypes of larger affinities, but new affinities are also known to crop up from time to time. 
The broad categories of affinities were defined based on the deities that first granted them, and are as follows, with examples of more specific affinities:

• Sun Affinities: Light, fire
• Frost Affinities: Water, moon
• Petal Affinities: Wind, lightning
• Wood Affinities: Plant, earth
• Marrow Affinities: Spatial, time
• Noon Affinities: Healing, emotional
• Evening Affinities: Transformation, mental
• Midnight Affinities: Shadow, illusion

There are two more broad categories that arose when members of the Inspired and Strength Triads began manifesting magic, those being:

• Magnetic Affinities: Gravity, metal
• Vital Affinities: Body enhancement, blood

In addition to type, affinities also have a strength - regular and strong. Those with a regular strength affinity can also learn low level spells of similar affinities - for example, a magic user with a fire affinity could learn light and smoke magic, or a magic user with a water affinity could learn ice or moon magic. 
Those with a strong affinity, however, can only learn magic of their specific type. However, their baseline magic strength is higher than a regular affinity user and they are often able to learn spells normally considered impossible - such as a flame that heals for a strong fire affinity user. 
There are also those with dual affinities, which is uncommon, and those with tri affinties, which is rare. While dual affinities are usually regular strength, tri affinities are almost always strong affinities - as the amount of power needed for regular strength tri affinities could easily overwhelm a mortal magic user's soul. 
There are also the disaffinited - those without any affinity. While unable to learn high level spells of any affinity, they are able to learn low and mid-level spells of any affinity. The disaffinited are the rarest of magic users. 

Combination and Personal Magic 

While affinities determine what general kind of magic someone can learn, there can be overlap in effects - those with blood and body enhancement magic affinities can heal others to a limited degree compared to a healing magic affinity, for example. A blood magic user can also use their blood to transfer knowledge to another, a skill usually associated with a mental magic affinity. 
This is an extension of the general understanding of personal magic - or rather, that having the same affinity does not gaurantee two magic users have the same spells or use their magic in the same capacity. A water magic user is also a sailor likely knows vastly different skills than a water magic user that is a combatant, or one that is an herbalist, etc. While they all have the capascity to learn each others' spells, they are unlikely to do so - most preferring either spells they enjoy or those that help them with their chosen profession. 
Disaffinited and those with dual and tri affinities often have an even higher variance in the spells know by a given individual - as the combinations possible using multiple kinds of magic are impressively large.

Type

Metaphysical, Arcane