Deities, or gods, are beings of immense magical power who operate on a level far above most magicians or magical creatures. They come in many forms and are as diverse as the humans who worship them, but can generally be charecterized by their nigh-invulnerability, extreme intelligence, and extremely advanced magical abilities.
The deities that have been shown all have a megalomaniac view of themselves. They all treat humans as though they are disposable and that sharing their seed is a gift. However due to their virtual immortality and great talent is it much of a surprise.
Though unconfirmed it would appear as though a God has a specific body as with ember and umber that can be destroyed. Raynard on the other hand seemed to be able to enter the body of another and work through them. It is unknown how this works.
It would seem that having the seed of a god inside of you gives you a lot more power than you can usually muster. This allows you to touch things that only a master magician can touch or cast spells of devastating strength. The effects of the seed ware off over time though.