the back of a body or object / to turn one's back / to hide something from / to learn by heart / to recite from memory / unlucky (slang) / hard of hearing
Yan, a vassal state of Zhou in modern Hebei and Liaoning / north Hebei / the four Yan kingdoms of the Sixteen Kingdoms, namely: Former Yan 前燕[Qian2 Yan1] (337-370), Later Yan 後燕|后燕[Hou4 Yan1] (384-409), Southern Yan 南燕[Nan2 Yan1] (398-410), Northern Yan 北燕[Bei3 Yan1] (409-436) / surname Yan
Green Wall of China, a massive afforestation program on the eastern margin of the Gobi Desert aimed at stopping the desert's expansion, started in 1978 and planned to be completed by 2050