A classical guitar was a type of guitar.
In 2024, when about to treat Cristóbal Rios's dislocated hand, Doctor Teresa Ramirez said if he wanted to be a classical guitarist, she'd better do so. He then replied that he never said anything about that, and she recommended he start playing the guitar. (PIC: "Assimilation")
In 2367, Geordi La Forge requested USS Enterprise-D's ship's computer play classical guitar music for his date with Leah Brahms. (TNG: "Galaxy's Child")