A "dan" rank signifies advanced skill or mastery in many Japanese traditions, as opposed to "kyu" ranks which signifies student or beginner ranks. This system was famously introduced to martial arts through Judo, where it is signified by a black belt. Further belt colors beyond black were later introduced to distinguish further "dan" ranks, including "coral" belts and red belts.

While it was introduced to martial arts by Judo, it is not specifies to martial arts and exists in other traditional Japanese practices such as calligraphy