What is "glaurung"

Glaurung is a fictional character in J. R. R. Tolkien's fictional Middle-earth legendarium. He is introduced in The Silmarillion as the first of the Dragons. He is also the main antagonist, along with Morgoth, in The Children of Húrin. He was known as The Deceiver, The Golden, The Great Worm and the Worm of Greed.