The Nephilim are beings that were created when a group of angels decided to join their essence of being with that of humans, with varied results. They are creatures of great size, and Uriel was given the duty of watching vigil over the until the time was right for them to be released. Though the Akashik records hold much information about them, I am limited in my access to that information, so I must apologize that I don't have much more in the way of detail. It would seem, though, that in two days, we will see for ourselves.