The balroq is a very large, winged, demon-looking creature.
It is best known from the movie "The Lord of the Rings: The Fellowship of the Ring," in which Gandolf the Gray battles a balroq on the Bridge of Khazad-dûm.
"suddenly it the Balrog
drew itself up to a great height, and its wings were spread from wall to wall..."
The Lord of the Rings Book II, Chapter 5 "The Bridge of Khazad-dûm".