Definition of "cryptogram"

It's a big help in solving cryptograms if you know how a cryptogram is constructed. The constructor normally uses two alphabets, one for plaintext, one for the substitute cipher letters.

1981, Norma Gleason, Cryptograms and Spygrams, Courier Corporation, page 7

To anyone who does not know the key, the five characters of the cryptogram are different but the genuine receiver is in no danger of confusion.

2002, Fred Piper, Sean Murphy, Cryptography: A Very Short Introduction, OUP Oxford, page 35

Indeed, Willaert was unable to read Charles's musical notation because it was actually a musical cryptogram passing for a madrigal, making absolutely no sense to a mere musician's naked eye, despite his towering talent.

2019, Ioanna Iordanou, Venice's Secret Service: Organizing Intelligence in the Renaissance, Oxford University Press, page 139

You already know this if you are an amateur codebreaker. On the comics pages of many newspapers, you will find a little puzzle known as a cryptogram. It's usually a famous quotation that has been encrypted in a very straightforward way […]

2007, Charles Seife, Decoding the Universe, Penguin