The Nyingma tradition is the oldest of the four major schools of Tibetan Buddhism (the other three being the Kagyu, Sakya and Gelug). "Nyingma" literally means "ancient," and is often referred to as Ngagyur (Wylie: snga 'gyur, "school of the ancient translations" or "old school") because it is founded on the first translations of Buddhist scriptures from Sanskrit into Old Tibetan in the eighth century. The Tibetan alphabet and grammar was actually created for this endeavour.
In modern times, the Nyingma lineage has been centered in Kham.
Example via www.ramdass.org: The 16th Karmapa, Rangjung Rigpe Dorje
Example via www.mindpodnetwork.com: Jiddu Krishnamurti Talks With Chogyam Trungpa Rinpoche