The term honkyoku means, 'music that was originally performed only on a specific instrument and which is the original music played on that instrument,' whereas the term "gaikyoku" means, 'music of a different type of genre that has been arranged to be played on a specific instrument not originally used in that genre.'
本曲は、「その楽器のみによる楽器本来の楽曲」を意味し、外曲は、「他種目の旋律をその楽器用に編曲した楽曲」を意味する。