In the Alien franchise, the derelict ship is found on the moon designated LV-426.
LV-426 is an exomoon associated with the planet Calpamos in later franchise material. In Alien, the world is largely unnamed on screen, but the Nostromo crew lands there after intercepting a mysterious signal. They discover the enormous derelict spacecraft and its cargo of eggs, setting the film’s catastrophe in motion.
The 1986 sequel Aliens established LV-426 as the moon’s familiar designation and introduced the colony of Hadley’s Hope there. The moon is also called Acheron, particularly in Aliens and expanded-universe material. That name can cause confusion, but LV-426 remains the catalog-style designation and is the standard quiz answer.
The ship itself is often called the Derelict. It belonged to the Space Jockey, later connected in franchise lore with the Engineers, whose corpse is found inside the vessel.