Definition and background:
Term used in Baroque music for a bass line that moves steadily in a rhythm contrasting to that of the upper parts.In jazz, a walking bass usually moves by steps played on bass or piano, with each note usually having the duration of a quarter note.
For more information on the music term "Walking bass" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary