The star and forge associated with the Dwarves in Avengers: Infinity War is called Nidavellir.
In the Marvel Cinematic Universe, Nidavellir is the home of the Dwarves, master weaponsmiths whose forge is powered by the intense heat of a dying neutron star. Thor travels there with Rocket and Groot after learning that he needs a new weapon capable of challenging Thanos. The journey forms one of Infinity War’s major parallel storylines.
When the group arrives, the forge has been shut down and most of the Dwarves have been killed by Thanos. Their king, Eitri, is left alive but unable to use his hands. Thor helps restart the star-forge, then risks his life holding the mechanism open so the star’s energy can pass through it. Eitri uses the heat to shape uru into Stormbreaker, Thor’s powerful new axe.
Nidavellir is sometimes described as a realm, a star system, or the name of the star-forge location, depending on the context. That terminology can cause confusion with Svartalfheim, another of the Nine Realms. In Infinity War, however, Nidavellir is the clearly intended answer for the Dwarves’ forge destination.