From the Wikipedia article :
Rou Gui (Chinese: 肉桂; Pe̍h-ōe-jī: bah-kuì) is a Wuyi Oolong tea; the name literally means Cinnamon. The tea can be difficult to prepare but its distinctive sweet aroma can be brought out up to 7 steepings. It was first developed during the Qing Dynasty.
This tea may be traditionally processed producing a dark dry leaf and a rich smell or processed according to new consumer standards, giving it a leaf of mixed color and a more fruity aroma.