Galaxia is just a normal sword in the games, which Meta Knight uses. In Kirby's Return to Dream Land; however, Kirby uses Galaxia when he has the copy abilty Ultra Sword. Other than that, Kirby uses a silver sword, not a golden one.
Galaxia is known as a legendary sword in the Anime. In fact, there's a whole episdoe about it. Episdoe 60: Crusade for the Blade tells about Galaxia's past, when a Star Warrior by the name of Silica (or Sirica) arrives in Dream Land and chases after Meta Knight to retrieve Galaxia.
Silica tells Tiff, Tuff, and Kirby about how Meta Knight and Garlude (her mother) venture into the cave of Kirisakin to retrieve Galaxia, since they were the bravest warriors. Meta Knight was able to retrieve Galaxia; however, Garlude was defeated by Kirisakin.