secret method; secret formula
General term for a confidential technique, recipe, or process, often in cooking, manufacturing, or magic.
このソースは代々伝わる秘法で作られています。
This sauce is made using a secret method passed down for generations.
esoteric rituals (Shingon Buddhism)
Specifically refers to the secret, esoteric practices in Shingon Buddhism, not a general secret method.
真言宗の僧侶は秘法を厳格に守っている。
Shingon Buddhist monks strictly observe the esoteric rituals.
彼はその手品の秘法を決して明かさなかった。
He never revealed the secret method behind that magic trick.
Compound of 秘 (secret) and 法 (method, law). The Buddhist sense is a specialized use of the same characters.