Single-strung
String instrument in which each note is produced by a single string, unlike double- or triple-strung instruments.
What it means
A single-strung instrument has exactly one string per note, unlike multi-course instruments, where two or more strings sound the same note together and are referred to jointly as a “course.” The modern classical guitar, for instance, is single-strung, since each of its six strings produces its own, independent note.
Musical use
The distinction between single-strung and multi-course instruments matters especially among plucked instruments, since multi-course forms such as many historical lutes or the mandolin produce a fuller, more overtone-rich sound through their simultaneously vibrating string pairs, while single-strung instruments sound clearer and more direct. Historically, some instruments moved from multi-course to single-strung construction, or the reverse, depending on the tonal ideal favored in a given era.
Being single-strung should be distinguished from an instrument's mere number of strings: even an instrument with many strings, such as the harp, is single-strung as long as each string produces its own note. A multi-course arrangement only arises when several strings are tuned and played together for the same note, as with the twelve-string guitar, whose strings are arranged in pairs, that is, in double courses.
Performance practice
On single-strung instruments, tune each string individually and independently, since no second string supports the same note and any inaccuracy becomes immediately audible. When switching between single-strung and multi-course instruments, for instance from a classical guitar to a twelve-string, consciously adjust your technique, since the full sound of paired courses calls for a different picking strength and fretting approach.