Air on a G string

There is a perfect explanation why this tune is called after a single violin string. Wikipedia says:

The original piece is part of Bach's Orchestral Suite No. 3 in D major, BWV 1068, written for his patron Prince Leopold of Anhalt sometime between the years 1717 and 1723.

The title comes from violinist Wilhelmj's late 19th century arrangement of the piece for violin and piano. By transposing the key of the piece from its original D major to C major and transposing the melody down an octave, Wilhelmj was able to play the piece on only one string of his violin, the G string.

The video shows a very nice performance of this tune by four trombones. They adapted the original arrangement a bit by playing the first repeat of the score on two trombones rather than the written four.
To get the arrangement for four trombones follow the link below, it's public domain and can be ditributed for free:

http://www.mutopiaproject.org/ftp/BachJS/BWV1068/air-tromb/air-tromb-a4.pdf