I've seen the term 'key hardened hash' used to describe a recommended way to tighten up password hashing. What does this mean? Can it just mean to use a pepper?
I'll suggest an answer to my own question. Perhaps I'm essentially helping to define a term that has been introduced elsewhere. If we take the definition of 'hardening' in security as:
hardening is any one of a variety of measures taken to make it more difficult for an intruder to circumvent the authentication process
Then 'key hardening' is any action with the intent of making it more difficult to act against the cryptographic hash function by introducing a cryptographic key that is used with the hash function. The standard means for doing this is using an HMAC https://en.wikipedia.org/wiki/Hash-based_message_authentication_code