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The violin has the most players in the orchestra, the bass has the most names. Double bass, string bass, bass violin and contrabass also accurately refer to this instrument. It is the largest and lowest-pitched bowed string instrument. Its relation to the violin family is contested. A direct descendant of the violone, the bass might be a legitimate heir to the viol family (which saw its heyday long before the violin was invented).
In the orchestra the bass supplies power, weight and rhythmic foundation. It entered the orchestra in the late 17th century. It often doubles the cello line one octave lower. In Pops concerts often one may hear a single bass playing what in jazz is known as a “walking bass line”: a series on notes that “walk” from one chord to the next.
As with the other instruments of the string family, the bow plays a crucial role. Bass players use one of two distinct bowing styles: one overhand as with the violin (French), the other underhand, as with a viol (German).
Source: The Norton/Grove Concise Encyclopedia of Music, edited by Stanley Sadie. London: Macmillan Press Ltd.,  ISBN 0-333-43236-3