Wikipedia
Honkyoku
Honkyoku (本曲, "original pieces") are the pieces of shakuhachi music played by mendicant Japanese Zen monks called komusō. Komusō played honkyoku for enlightenment and alms as early as the 13th century. Honkyoku is part of the practice of suizen (吹禅, "blowing Zen"). The Fuke sect which originated this practice ceased to exist in the 19th century, after which several shakuhachi guilds were formed, and the verbal and written lineage of many honkyoku continues today, though the music is now often practised in a concert or performance setting.
There are many ryū, or schools, of honkyoku, each with their own style, emphasis, and teaching methods.