From the FRCG:
The Feywild is a magical and mysterious echo of the world. Called Faerie in ancient texts and Elven works, the Feywild is home to countless fey, and the origin of Toril’s elves and eladrin and their deities. Its relationship to the world has waxed and waned over the millennia. During bygone times, eladrin built secret realms in Faerûn more closely connected to the Feywild than was the case in the rest of the world. Perhaps through these connections, the Spellplague pulled the Feywild back into Toril’s proximity. The Feywild is a twilight realm of stunning natural beauty and raw magic. Its landscapes are full of splendor and danger foreign to the mortal world. Many of its creatures have existed in the world for ages, but not in so terrible and organized a form as they do in the Feywild. Some correspondence exists between worldly terrain and the fey lands. Although not every feature of Toril has a twin in the Feywild, many do.
See Manual of the Planes, pg 32 for more details on the Feywild.