Pu-erh or Pu'er tea is a variety of fermented dark tea produced in Yunnan province, China. Fermentation is a tea production style in which the tea leaves undergo microbial fermentation and oxidation after they are dried and rolled. This process is a Chinese specialty and produces tea known as Hei Cha, commonly translated as dark, or black tea.
Pu'er traditionally begins as a raw product known as "rough" Mao Cha and can be sold in this form or pressed into a number of shapes and sold as "raw" Sheng Cha. Both of these forms then undergo the complex process of gradual fermentation and maturation with time. In the mid-1970s Tea Factories created a new type of pu-erh tea, with a process that involves an accelerated fermentation into "ripe" Shou Cha which is then stored loose or pressed into various shapes; this is the most common type of pu-erh readily available.