Fae (n): The magical creatures that inhabit Oris.

First, on the difference between magical and natural creatures. A natural creature can use magic and produce magic. A natural creature is an individual born with a soul and a lifespan. It has a memory and learns to interact with its environment. It is born of reproduction, and may also reproduce, and it will eventually die. It must consume to continue producing energy. A magical creature is magic. A magical creature has no soul or lifespan. It is born of magic and is only a manifestation of magic. It will not die, but it can be killed. It may simply cease to exist after a while. Some magical creatures are created by individuals. Others are simply created by the flow of mana.

Creatures that are created from the flow of mana, or life energy, are known as fae. Faeries, dryads, nixes, jinns - all these are manifestations of  the flow of mana. Fae are bound to the mood of the mana they are born of. Faeries from the grasslands and flowers, dryads from the forests, nixes from the streams, jinns from the badlands, etc... These fae exist in the world as a part of it. They are generally neutral towards humanoids in general, but they are given to moods. Faeries in particular are given to the playful moods that fill the sunlit  meadows; most of their mischief means no harm. Similarly, water spirits usually do not mean to drown people - they'd not think of the place they're born of as being bad for something. They only mean to share, as it is the mood of the water to share. Fae will protect the place or thing they are borne of if they feel it is threatened. Fae can be slain, but new fae, or maybe the same one if you choose to believe, will be born in its place. Just as fae are born when the flow of mana feels like it, so they can disappear when the flow of mana no longer considers them necessary. In this manner, how many fae there are depends on the mood of the world.

Drae (n): Decidedly malevolent fae.

Fae can be born of the mood of a place of trajedy, and will therefore be bound by hatred or some other malevolent feeling. Such a creature is called a "drae." Trolls, goblins, wights, hags... These are born in places scarred by ill-feelings and travesties. Battlegrounds often bear drae that devour the corpes and go on to hunt more men. These can be killed, but they will continue to rise in the scarred places until the mana stream is healed. Ghosts and wraiths come from similar moods. They will not actually be the tormented soul of the murdered, for the soul always passes on, but rather a manifestation of the feelings of the person just before their death.

Demi-Fae (n): A species of fae that exhibit natural properties, or a species of natural creatures that exhibit magical properties.

There are several ways that demi-fae come into existence, but the two most common are: The resulted breeding of a natural and magical creature, or a magical creature that gains a soul.