course

On a musical instrument, a group of strings which are tuned to the same pitch and are played as one string. Lutes, some guitars, and mandolins have double courses, harpsichords have triple courses, and pianos range from heavy single courses in the bass to quadruple courses in the extreme treble. The 12-string guitar is a modern example of a double-course instrument, each pair tuned to the octave rather than to the unison.

While the original purpose of doubling of strings may have been to increase loudness, an additional factor is improved liveliness of tone caused by beat interference of near-unison strings, an important factor in the tuning of a modern concert grand piano.