Specifically refers to the string of a shamisen or similar traditional Japanese stringed instrument; the kanji 絃 is used for this musical context, while 弦 is more general.
See also: 弦 (げん)
The shamisen string broke, so I put on a new one.
Metonymic use: the string stands for the whole instrument. Rare and mostly found in poetic or traditional contexts.
He picked up the stringed instrument and began to play quietly.
geisha; female entertainer (shamisen player)
five-stringed instrument; pentachord
The kanji 絃 is composed of 糸 (thread) and 玄 (dark/mysterious), suggesting a thread that produces deep sounds. It is a specialized character for musical instrument strings, distinct from the more general 弦.