What is the X in X-mas?
any of the genres for solo voice and voices in combination, with or without instrumental accompaniment. It includes monophonic music (having a single line of melody) and polyphonic music (consisting of more than one simultaneous melody). This article deals with Western art music preserved in staff notation, either for a single solo voice or for voices in unison, and briefly discusses the differences between Western and non-Western traditions. It excludes the complex forms of opera, oratorio, cantata, mass, and requiem, in which solo singing is frequently combined with choral music. The earliest written examples date from the 10th century, prior to which music was transmitted principally by oral tradition.