Neldoreth, otherwise known as the Forest of Neldoreth, was a forest located in the area of Doriath.
Neldoreth was amongst the many areas of Doriath that was enclosed within the Girdle of Melian after the First Battle of Beleriand. Lúthien was born here to Thingol and Melian during the Years of the Trees and the Sleep of Yavanna in Middle-earth. It was also the place, during the First Age, in which Beren first saw Lúthien as she danced in the moonlight and fell in love with her.
After Beren was captured by Sauron, Thingol, knowing that Lúthien would try to rescue him, had her imprisoned in a house built in the tallest Beech-tree which the Sindar of Doriath called Hírilorn.
Neldoreth is a Sindarin word with obscured meaning. The first element of the word Neldoreth came from the word neldor, meaning 'Beech-tree', though the origin of the second element eth appears to be unclear. It may have originated from the Sindarin words eryn, meaning 'forest', ethuil, meaning 'spring', or eth, which is an ending referring to a person or an animal. From these words, the word Neldoreth could mean "forest of Beech-trees", "spring of Beech-trees" (or perhaps "the growing of the Beech-trees"), or "Beech-trees of animals" (or it may have been a reference to the Elves of Doriath, in which case it could have the intended meaning of "Beech-trees of the Elves", or perhaps it was a reference to both Elves and animals).