LOTR: What Are the Nameless Things?

From the Hobbits to the Fell Beasts, the rich lore of The Lord of the Rings comprises several different races, each with their own mythology and backstory. However, J. R. R. Tolkien also includes many characters with unexplained origins (some more intentionally than others), which also the mysterious entities, the Nameless Things. Little to nothing has been shared about them in The Lord of the Rings series, and even Gandalf refuses to divulge any information about his encounter with them. While he is fighting with Durin’s Bane in TA 3019, they both fall from the Bridge of Khazad-dûm into a deep chasm.