The Six Secret Teachings and The Three Strategies of Huang Shigong
Refers specifically to two ancient Chinese military classics: 六韜 (Rikutō) and 三略 (Sanryaku). Used in historical or literary contexts.
He thoroughly read The Six Secret Teachings and The Three Strategies and mastered the secrets of military strategy.
secrets of the art of war; mysteries of strategy
Figurative extension: refers to profound knowledge or secrets of military tactics, or more broadly any arcane expertise. Often used in the phrase 六韜三略を極める.
He knows all the secrets of the trade.
兵法 is a general term for military strategy or tactics, while 六韜三略 specifically refers to the two classic texts or their teachings.
奥義 means 'secret principles' or 'esoteric techniques', often in martial arts or arts. 六韜三略 is more specifically tied to ancient Chinese military classics.
From the titles of two ancient Chinese military treatises: 六韜 (Rikutō, 'Six Secret Teachings') and 三略 (Sanryaku, 'Three Strategies'). The compound is used as a yojijukugo to refer to these works or, by extension, to profound strategic knowledge.