The sword Bilbo gives to Frodo in J.R.R. Tolkien’s The Lord of the Rings is called Sting.
Bilbo acquired Sting during the journey described in The Hobbit, when he and the dwarves discovered weapons in the trolls’ hoard. Although small by the standards of human swords, it was an Elvish blade from Gondolin and proved useful to Bilbo. He later passed it to Frodo before the quest began.
Sting has a distinctive supernatural property: its blade glows blue when Orcs or other enemies associated with them are nearby. Frodo uses it during dangerous encounters, including the confrontation with Shelob. The weapon is therefore both a practical sword and a warning instrument.
Sting is often confused with other famous blades in Tolkien’s legendarium. Glamdring belonged to Gandalf, Orcrist was carried by Thorin, and Narsil was the sword of Elendil. In the book, Bilbo’s sword is also the source of the name he gives it, reflecting its small, piercing character.