The secret soup is the key to this shop's ramen.
I learned a secret technique from my master.
秘伝 is the secret technique or recipe itself (a noun for the content), while 伝授 is the act of teaching or passing that secret on.
Compound of 秘 (secret) and 伝 (transmit). The exact historical derivation is uncertain, but the word has been used since at least the Edo period to refer to esoteric teachings passed down orally or in writing.