The double bass was a musical instrument design that used four strings. These strings were stretched from the tip of a billfish beak, running down over a skin stretched tautly across a wooden frame. The wooden structure was propped up by three bone legs. To play the double bass, a bow was used, which was just string stretched between the ends of a curved piece of wood. This instrument was crafted by the Lanai species on their native homeworld of Ahch-To, and one such instrument was owned by those who lived in the Caretaker village on Temple Island.
For the movie Star Wars: Episode VIII The Last Jedi, a double bass prop was built, but the scene featuring it was removed before the film was released. The instrument was still included in Star Wars: The Last Jedi: The Visual Dictionary, a companion book written by Pablo Hidalgo that was released with the film on December 15, 2017.
The double bass, also known as the contrabass, exists in reality, but its design is quite different.