also Shang Shung, or in modern Chinese: Xanxun
Name of an ancient Himalayan kingdom that existed before (ca. 500 years earlier) and during
the rise of the kingdom known as Bod (Tibet).
Zhang Zhung roughly covered the area now known as West Tibet, specifically Guge and the region around Mt. Kailas (Tib., ti se) and Lake Manasarovar (Tib., ma-pham tsho), and Ladakh (now a part of Indian controlled Kashmir).
Once the Bod-kingdom had expanded into all directions - to the borders of Turkestan (north) and Persia (west) to parts of Nepal (south) and to Amdo (east) - also Zhang Zhung became a part of Bod, which by then had grown into what we are now accustomed to call Tibet.
Although there is no exact history (yet) of Zhang Zhung and its cultural development, it seems that Buddhist and Tantric teachings have reached this area and merged with the indigenous tradition - a development that occurred way before the so-called first diffusion (of Buddhism into Tibet).
This is also indicated by the title of a genealogy of the Dzogchen teachings within the Bon tradition: Dzogchen Zhang Zhung Nyangyud (Tib., rdzogs-pa chen-po zhang-zhung snyan-brgyud) translates as The Oral Transmission of the Great Perfection of Zhang Zhung; also known in a short form as Zhang Zhung Nyangyud.