The Feywild is a parallel plane of Halcann where magic and nature flows unchecked. The Feywild was first discoverd by the precursor elf during The Rule of Dragons where a The Last Flight becoming the Eladrin.
Flow of time
Time flows much slower in the Feywild, with a day in the Feywild equalling to roughly a week in the real world, leading to the Eladrin and its other inhabitants to have a vastly different concept of time and concerns compared to those of the Material Plane.
A place where Halanna survived?
It is widely accepted that the creator deity Halanna died during the Godswar but some theorists and wood elven druids suggest that the Feywild was in reality the swan song, the final creation, of Halanna in which she transported her spirit into what the Eladrin and wood elves refer to as the Mother Tree. The worship of the Mother Tree now forms the basis of the Cyranvari Commune, the religion of wood elves.