Please avoid use of the term "key" without explicit qualifiers

The OpenPGP ecosystem has many different things that are called "keys". There are at least:

• transferable public key (a.k.a. "certificate")
• transferable secret key
• public key packet
• subkey packet
• cryptographic key material (without any packet framing)

I think this draft will be easier to read if everywhere it says "Key" with no qualifier, it uses either an explicitly qualified variant of "key", or an entirely different word.