A musical cryptogram is a cryptogrammatic sequence of musical symbols which can be taken to refer to an extra-musical text by some 'logical' relationship, usually between note names and letters. The most common and best known examples result from composers using musically translated versions of their own or their friends' names (or initials) as themes or motifs in their compositions. These are not really rigorous cipher algorithms in the formal sense, but more like musical monograms. The methods used historically by composers were either too incomplete (i.e., did not include all of the letters of the alphabet) or too simplistic to meaningfully encrypt long text messages. There is a separate history of music ciphers utilizing music notation to encode messages for reasons of espionage or personal security that involved encryption and/or steganography.
Because of the multitudinous ways in which notes and letters can be related, detecting hidden ciphers in music and proving accurate decipherment can be difficult.