Bilbo Baggins’s sword in J.R.R. Tolkien’s books is called Sting.
Bilbo finds Sting in a troll hoard during The Hobbit, along with two larger Elvish blades. Because the sword is small enough for a human-sized person to use, Bilbo adopts it as his own. Its small size is appropriate for a Hobbit, though it is still a powerful and ancient weapon.
Sting has a distinctive magical property: its blade glows blue when Orcs or Goblins are nearby. Bilbo uses it during his adventures, and later gives it to Frodo. Frodo carries Sting during the journey to destroy the One Ring, including into Shelob’s lair.
A common mix-up is to call Bilbo’s sword Glamdring or Orcrist. Those are the other two blades found in the troll hoard. Gandalf takes Glamdring, while Thorin Oakenshield claims Orcrist.