Guitar
From Memory Alpha, the free Star Trek reference.
The guitar is a stringed musical instrument originating from Earth.
20th century musician L.Q. Clemonds played the guitar. (TNG: "The Neutral Zone")
When Geordi La Forge wanted to impress Doctor Leah Brahms who was about to visit him in his quarters, he decided to play a piece of music played by a classical guitar. (TNG: "Galaxy's Child")
In order to pass the time while en route to Risa in the type 15 shuttlepod Onizuka, La Forge listened to a piece of music played by a Spanish guitar. (TNG: "The Mind's Eye")
Data sometimes played the guitar in his quarters. (TNG: "Silicon Avatar")
One member of the mariachi band that Q conjured up in order to thank the crew of the USS Enterprise-D for taking care of him while his omnipotence was taken away, played a large bass guitar, also called a guitarron. (TNG: "Deja Q")
[edit] Background Information
The script of the Star Trek: Deep Space Nine episode "Melora" described the Klingon chef's musical instrument as being "a Klingon guitar" with "a strange steel guitar-type sound" emanating from it.
