Transcription (music)
Sometimes transcriptions are made for practical reasons. Mozart made transcriptions of some music from his own operas, arranging them for small groups of instruments so that they could play it for popular entertainment.  Stravinsky transcribed some of his ballet music for piano, e.g. The Rite of Spring for piano duet and some dances from Petrouchka for piano solo. These types of transcriptions are often referred to as a "reduction": the simplification of a large work to be performed by a smaller ensemble or a soloist.