Hei Cha (黑茶) translates into Black Tea in English, but it is actually a class of teas different from the traditional understanding of 'black tea'.
Based on the level of enzymes involved oxidisation or fermendation occurred during the tea processing, teas are categorised into: green tea (绿茶), white tea(白茶), yellow tea(黄茶), Oolong tea (乌龙茶), black tea (红茶) and Hei Cha (黑茶).
As one can see, the black tea above is actually 红茶 in Chinese, which means 'red tea'. This leaves the Hei Cha (黑茶) being a different categoy all together. Hei Cha is defined as a category of teas that are ofent compressed (not all) with a unique characteristic of post-fermentation. The name Hei Cha (黑茶) is the result of the dry tea leaves often have a very dark to black appeareance.
Various natures of Hei Cha (黑茶):