A 'Shai Hong' black tea. Also known as a sun-dried black tea in the West. It's special type that combines the black tea and pu erh tea processing methods. Basically the leaves are processed using the black tea method except for the last sun drying step, which is taken from the method of producing sheng pu erh:
Sun Dried Black Tea Block
I've read a post about my experience on Shai Hong if you're interested.