“Six Secret Strategic Teachings”, one of the Seven Military Classics of ancient China 武經七書|武经七书[Wu3 jing1 Qi1 shu1], attributed to Jiang Ziya 姜子牙[Jiang1 Zi3 ya2]
Definitions (Wiktionary)
name
Six Secret Teachings, treatise on civil and military strategy attributed to Jiang Ziya