鐵 is iron, and 觀音 is the Chinese name for the Buddhist goddess of compassion, so 鐵觀音 is iron goddess of compassion.
Often listed by its Mandarin pronunciation, Tieguanyin, this the most popular oolong tea from Anxi (often listed as one of the Chinese Top Ten Famous Teas), a county in Fujian province known for oolong teas.