An instrument with at least one (multiple string) course is referred to as coursed, while one whose strings are all played individually is uncoursed.
Multiple string courses were probably originally employed to increase the volume of instruments, in eras in which electrical amplification did not exist, and stringed instruments might be expected to accompany louder instruments (such as woodwinds or brass). Eventually, however, they came to be employed to alter the timbral characteristics (the "tone") of instruments as well.
Strings within a multistring course may have all the strings tuned to the same pitch (e.g. mandolins); they may be tuned to the same pitch class but in different octaves (e.g. Tiple); or the strings may be tuned to different pitches, usually for special effect.
Examples of instruments that use two-string courses include:
Examples of instruments that use three-string courses include: