Pu-erh tea, also spelled as Pu'er tea is a variety of post-fermented tea produced in Yunnan province, China. Post-fermentation is a tea production style in which the tea leaves undergo a microbial fermentation process after they are dried and rolled. This is a Chinese specialty and is sometimes referred to as dark, or black tea (this type of tea is completely different from what in West is known as "black tea", which in China is called "red tea"). There are a few different provinces, each with a few regions, producing dark teas of different varieties. Those produced in Yunnan are generally named Pu'er, referring to the name of Pu'er county which used to be a trading post for dark tea during imperial China.