Definition and background:
A characteristic of Baroque music consisting of a bass part that runs continuously throughout a work, also called thoroughbass. If it is figured to indicate the harmony, it is called figured bass.Continuous bass; i.e., a bass part played continuously throughout a piece to give harmonic structure, used especially in the Baroque period.Figured bass commonly used in music of the baroque period. It was the normal practice to make use of a bass instrument of some kind, for example a cello or bass viola da gamba and a chordal instrument, a keyboard instrument or plucked string instrument, the part of the latter indicated by numbers added to the music for the bass instrument, showing the chords as a basis for improvised accompaniment or 'filling in' and embellishing of harmonies.
For more information on the music term "Basso continuo" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary