Tibet was an Asian region located in China, on Earth. The Tibetan plateau was located in Tibet. (DS9: "Our Man Bashir")
Jack, a youth from Carbon Creek, Pennsylvania, preparing for college spent a lot of time at the library about places he'd like to visit, including Tibet. While discussing meditation with T'Mir in 1957, Jack explained to her that his readings, he learned that the Buddhist monks of Tibet meditated every day. (ENT: "Carbon Creek")
In 2151, Captain Jonathan Archer claimed that the oldest monastery that he ever visited was in Ngari, Tibet. (ENT: "The Andorian Incident")
While visiting Earth during the mid-22nd century, Doctor Phlox attempted to familiarize himself with many of the planet's religions including Buddhism, which he accomplished by spending two weeks at a Tibetan monastery where he learned to sing chords with the high lamas. (ENT: "Cold Front")