The sword Bilbo finds in the troll hoard in J.R.R. Tolkien’s The Hobbit is Sting.
Bilbo discovers Sting along with two larger Elvish blades after Gandalf, Thorin, and the Dwarves find the trolls' hoard. Because the sword is short enough for a Hobbit to use, Bilbo adopts it as his weapon. Its blue glow later warns him of nearby Orcs or Goblins.
Bilbo initially does not know the weapon's history. It was forged by Elves in Gondolin during the First Age, making it vastly older than Bilbo's adventure. After Bilbo gives it to Frodo, the sword remains important during the journey to Mordor.
Glamdring and Orcrist are the other two famous blades from the troll hoard. Glamdring becomes Gandalf's sword, while Orcrist is claimed by Thorin. Andúril belongs to Aragorn and is reforged from Narsil much later in the legendarium.