A compound passphrase is a password consisting of a combination of 12 to 24 English or Japanese words.

Example: apple dog cat go paper cap water hand tree…

Q. When do I use the recovery passphrase?

A. I lost my smartphone, which had a wallet app installed on it!
I've forgotten my wallet's private key!
I use it sometimes.

If you have a recovery passphrase, you can recover the assets in your wallet in situations like the one described above.
Conversely, if you lose your composite passphrase, you will be permanently unable to access the assets in your wallet in the situations described above!
On the contrary, if your recovery passphrase is stolen, your wallet could be recovered and your assets stolen.

Just like your private key, this is something you should never tell anyone!
Please be careful!