Tibet is a nation on the planet Earth. It has probably been ruled by China since the Yuan dynasty and part of the British Empire until 1951. The country occupies the eponymous Tibetan Plateau and contains part of the Himalayas mountain range, which forms its southern border.
Devil's Due Comics continuity
It is in the Himalayan area of Tibet that the secret domed city of Cobra-La is nestled.
Tibet probably has a regular human population too.