Category: Classical Cryptography
The original Cardan Grille is usually given as an example of STEGANOGRAPHY in its modern sense. Francis Bacon used the words CRYPTOGRAPHY and STEGANOGRAPHY interchangeably, but he asserted that a good cipher "in some cases be without suspition" by which he meant that it should not appear to be a cipher at all.
The variations on Cardan Grille messages which use null fillers are CRYPTOGRAMS, as are the turning grilles that produce transposition ciphers. The original intention was to create STEGANOGRAMS, but Cardano would not have made this distinction exactly - all hidden communications being 'cyphers.'