Forms of Magic
This information is gleaned from various bits of Warcraft lore, but does not necessarily represent official information.
Two categories of magic exist, arcane and divine. Divine magic contains druidism, shamanism, voodoo, and holy light, as well as other religions. Nature is a subcategory within the divine, but a form of it can also be found in arcane as well. Runes are mystically ancient, it is a type of arcane magic, but accessed by more natural means (see Runemasters and Inscribers).
Arcane
Arcane is the most common form of magic. Used by mages, wizards, and other sorcerers, such as those of the Kirin Tor, arcane magic is ever present in the atmosphere and accessible to any who are capable of drawing upon its energies. Arcane magics were discovered by the Kaldorei and later refined by the high elves of Quel'thalas and the human nations, and are most commonly practiced by mages.WRPG 150-151 WoWRPG 59
Arcane magic comes from the Well of Eternity, which itself draws from the Twisting Nether. Arcane magic is very powerful, but if not used carefully can cause corruption and great destruction. WoWRPG 248-249
Druidism
Another nature-reliant class, druids derive their power from the earth itself, although they do not require totems to channel energy like shamans. They become agents of nature itself, forming a bond with all beings of nature and pulling their strength directly from that bond. Night elves were taught druidism by Cenarius.WRPG 154 Only beings who are directly attuned with nature are capable of adopting the power of a druid.
Fel
The term Fel refers to the magics used by demons, more specifically, the Burning Legion. Fel energy is arcane magic at its most corrupt. If arcane magic is an addiction, fel magic is the embodiment of the drug at its purest form.
Geomancy
Geomancy is a practice of divination and elemental combat native to several humanoid races of Azeroth. It is similar to shamanism in that disciples of geomancy wield the powers of the earth and encourage respect of earth’s spirits. The main difference between a geomancer and a shaman is the method through which the trust of the elements is gained. A shaman speaks directly with the elemental spirits, whereas a geomancer uses rituals, songs, and sacrifices to appease and propitiate the spirits.
Holy/Light
This magic was originally practiced by the Clerics of Northshire, a priesthood in the earlier days of Stormwind. The clerics and priests who practiced it believed their magic came from belief in the Holy Light, a set of ideals the church dedicated itself to. WRPG 155 This form of divine magic is used to protect and heal, and comes from the naaru. Divine magic was later practiced by The Silver Hand, the group of Paladins who developed a melee-based hybrid form of the magic.
Necromancy
Necromancy is similar to the magics used by warlocks, however, instead focuses on the study of death rather than demonology. They are capable of reviving living creatures from death to do their bidding as undead servants.
Runic
Runic magic was created by the titans. Their creation, the dwarves, quickly mastered the mysteries of the runes taught to them. However, as generations passed, the dwarves forgot their heritage and lost all knowledge of runes and their hereditary powers.
Tauren in Kalimdor rediscovered the power of runes. An ancient race as well, the tauren remembered the myths of runecasting and revived interest in this nearly lost art. The dwarves that came to Kalimdor with Jaina Proudmoore's Alliance Expedition learned tauren runecasting techniques. Tauren and dwarves do not share good relations, but they were eager to share knowledge of runes and titan myths.
The Vrykul practice a runic magic that even the most experienced wizards find unfamiliar.
Shamanism
The shaman's power is drawn from spirits, both of ancestors and of spirits found in natural surroundings.WRPG 154-55 Shamanism is also practiced by some of the draenei who learnt shamanism on Draenor. In modern history, shamanism is common among orcs, tauren, trolls and draenei.
Voodoo
Voodoo is a strange tribal mix between the power of arcane and divine magic,LoC 117 practiced by witch doctors and shadow hunters. They often combine reagents in a cauldron to create strange brews that most often result in bizarre transformations when consumed. They are widely known for placing hexes to morph victims into various creatures or placing curses.M&M 55-57 HPG 66-68 The majority of voodoo users are trolls, although other races of the Horde have taken up the craft.