Puerh tea (Pu'er tea / 普洱茶) is officially defined as a sun-dried tea produced from the large leaf varietal (Camellia Sinensis var. Assamica) of tea trees growing in Yunnan province, China. This tea typically undergoes post-fermentation through microbial and oxidative processes and continues to change and evolve with age. In the past 15-20 years it has become very well known and popular throughout China and South-East Asia, with the finest aged examples fetching astronomical prices at auction and the most sought after fresh teas in such demand that they rarely make it onto the open market.
Puerh tea is generally defined as being from China's Yunnan province. As the traditional cultivation and processing of this type of tea isn't limited to political boundaries there have been similar teas produced in Northern-Western Vietnam, Northern Laos and Myanmar. In general though we can limit the scope of our conversation to the south-west of Yunnan province.