The ''yu'' was a free reed wind instrument used in ancient China. It was similar to the , with multiple bamboo pipes fixed in a wind chest which may have been made of bamboo, wood, or gourd. Each pipe contained a free reed, which was also made of bamboo. Whereas the sheng was used to provide harmony , the ''yu'' was played melodically. The instrument was used, often in large numbers, in the court orchestras of ancient China but is no longer used.
A third-century BC line drawing featuring a ''yu'' player may be seen .
Although the ''yu'' is now obsolete, it is known to most Chinese speakers through the saying "Làn yú chōng shù" , meaning "to fill a position without having the necessary qualifications." The saying is derived from the story of Nanguo, a man from southern China who joined the royal court orchestra of King Xuan , the ruler of the as a ''yu'' player. Although the man did not actually know how to play this instrument, he knew that the orchestra had no fewer than 300 ''yu'' players, so he felt secure that he could simply pretend to play, and thus collect a musician's salary. Upon the king's death, Nanguo was eventually found out as an imposter when the king's son Min , who had succeeded his father as king, asked the musicians to play individually rather than as a group. On the night before he was to play, Nanguo fled the palace, never to return.
The ''yu'' is similar to the ''lusheng'', a free reed mouth organ used by various ethnic groups in several provinces of southern China.