You say that like it's that big a leap. In any case, sorry I wasn't 100% linguistically perfect, even post-elaboration. Half of people say I should be concise, the other half says I should elaborate more, so I figured someone would sound unpleased.
The "key" is the mapping of cipher alphabet to message alphabet.
There has to be a secret to be cryptography. The meaning has to be hidden without the secret information (though primitive/weak attempts can have a small enough search space to be brute forced). But the content being hidden without that information is the entirety of what the word means.