That's a poor definition. If I read someone's GPG password off a Post-It on their desk, I can decrypt any information encrypted with it, but I'm not authorized

That's a poor definition. If I read someone's GPG password off a Post-It on their desk, I can decrypt any information encrypted with it, but I'm not authorized to do so. A better definition would distinguish between those in possession of both the algorithm and all its inputs, and those who aren't in possession, and rather than saying they "cannot" access the encoded information, it would say that access is impractical or at least cumbersome. By that better definition, it's still encryption, because it made it cumbersome for someone to access the codes without understanding the encryption method.