The Blackened Woods is the name of a large region in Quel'Thalas, or all of Quel'Thalas, made up of the current Ghostlands and most, if not all, of Eversong Woods. The region was formerly known as Eversong Forest. The region was renamed Blackened Woods after the forest was burned down by red dragons during the Second War, and then by the blood elves after the Third War.
This whole region also gained the title Ghostlands of Quel'Thalas, in addition to its previous designation, after it was ransacked by the Scourge. Eversong Woods represents land that was taken back and recultivated, whereas the current Ghostlands region represents an area that is still sickly or burned. It lies just south of the Silvermoon region, a region which includes Silvermoon City and Quel'Danas (and possibly parts of Eversong Woods).
Blackened Woods is a land burnt and covered with ash and sorrow. Forlorn ruins jut from the ground and black trees stretch into the distance. Wispy elven spirits flit among them. This forest suffered dragonfire in the Second War and the Scourge’s ravages in the Third. Finally, the surviving high elves, calling themselves blood elves, resolved that the undead would not enjoy their victory and put the trees to the flame.