Continual bass. A musical part consisting of a bass line
plus numbers to indicate the chord sequence; on lute, guitar,
or keyboard instruments, the bass line is played on the lower strings, while the right hand improvises around the given chord sequence.
Used mostly for baroque music, but the same kind of notation occurs in all sorts of music.
The chord sequence indicates harmonic sequences, but if Webster 1913 states that harmony is a synonym,
it commits a mistake of category.