In Star Wars: Return of the Jedi, the forest moon where the second Death Star is located is Endor.
The second Death Star, designated DS-2, is built in orbit above Endor. Its shield generator is installed on the moon’s surface, hidden in an Imperial bunker. The Rebel Alliance sends Han Solo, Princess Leia, Chewbacca, and their strike team to destroy that generator while the fleet attacks the battle station in space.
Endor is home to the Ewoks, whose knowledge of the forest and resistance to Imperial occupation become crucial to the ground battle. Once the Rebels disable the shield, Lando Calrissian and Wedge Antilles lead the assault into the station, helping destroy the reactor and the incomplete superweapon.
Viewers sometimes call the location simply “Endor,” but the original film specifically emphasizes the forest moon of Endor. The wider Endor system includes a host planet and other moons; Kef Bir, an ocean moon, is where the Death Star wreckage appears in The Rise of Skywalker.