What is the ranking term 'dan' specifically used for?

The term 'dan' is specifically used to denote advanced ranking levels in martial arts, particularly in disciplines such as Taekwondo and Karate. It signifies a level of proficiency that is above the kyu ranks, which are typically assigned to beginners and intermediate practitioners. Achieving a dan ranking usually requires a combination of skill, experience, and time spent training, in addition to successfully passing tests or demonstrations of technique and knowledge. Dan ranks are further subdivided into numbers (like 1st dan, 2nd dan, etc.), indicating progressive levels of expertise and mastery. Thus, the correct option identifies 'dan' as representing mastery levels in martial arts.