The Burning Forest, sometimes abbreviated to bf, is the name of an area in FoW.
Slaves of Menzies
This quest, often shortened to "Slaves", is given by Miko the Unchained, and takes place in the forest. 4 Shadow Overlords spawn at the north-eastern end of the forest, and the goal of the quest is to kill them all.
West of the forest is a path leading to the Battlefield, and to the south is ToS. The enemies in the forest are mostly Mahgo Hydras, Smoke Walkers, and Ancient Skale, but there are also Abyssals, Shadow Rangers, and Shadow Mesmers in the quest area, and a Shard Wolf spawns in the middle of the forest. None of these foes are hostile to each other or the Skeletals on Battlefield, but they will fight the Shadows from ToS.