A course, on a stringed musical instrument, is either one string or two or more adjacent strings that are closely spaced relative to the other strings, and typically played as a single string. The strings in each multiple-string course are typically tuned in unison or an octave.
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Normally, the term course is used to refer to a single string only on an instrument that also has multi-string courses. For example, a nine-string baroque guitar has five courses: most are two-string courses but sometimes the lowest or the highest consists of a single string.
An instrument with at least one multiple-string course is referred to as coursed, while one whose strings are all played individually is uncoursed.