Variations (music)
George Frideric Handel wrote a famous set of variations for harpsichord called Harmonious Blacksmith, and Johann Sebastian Bach wrote the Goldberg Variations, which was a set of 30 variations: a very long piece of music.  It was written for a man who found it difficult to sleep at night, so he would ask his harpsichord player, whose name was Goldberg, to play to him.