A password, you mean?

More like a Shibboleth: https://en.wikipedia.org/wiki/Shibboleth

In the broad sense of a shared secret, yes

The text calls it a codeword:

> The solution the world's leading experts have landed on is one your grandparents could have come up with: codewords. You, your family, business partners and anyone else you communicate with about important subjects need to come up with a secret phrase that no-one else knows you can use in an emergency to verify each other's identities. Think of it like a convoluted form of the multi-factor authentication we all use to login online.

> "My wife and I have a codeword that we use if we ever get an unusual call," Farid says. "We haven't needed to use it yet, but sometimes I ask just to test her to make sure we don't forget it."