What is the name of the forest realm ruled by Thranduil in Tolkien’s Middle-earth?

The forest realm ruled by Thranduil in Tolkien’s Middle-earth is the Woodland Realm.

The Woodland Realm occupies the northern part of the great forest called Greenwood the Great. After the shadow of Dol Guldur spread through the southern forest, Greenwood became known as Mirkwood. Thranduil, a Sindarin Elf king, ruled the woodland Elves from his underground halls in the northern forest.

In The Hobbit, Thorin Oakenshield and his companions are captured by Thranduil’s Elves while crossing Mirkwood. Bilbo avoids capture by using the One Ring, then helps the dwarves escape in barrels down the Forest River. Thranduil later appears during the Battle of the Five Armies.

The Woodland Realm is distinct from Lothlórien, the Elven land ruled by Galadriel and Celeborn. It is also different from Fangorn, an ancient forest associated with Ents, and the Old Forest near the Shire. These locations belong to separate regions and have different rulers or inhabitants.