system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Different degrees in martial arts, what does it mean to be an 8th degree black belt?
gpt
In most of the modern martial arts that use a belt system (judo, karate, taekwondo, etc), a black belt signifies an advanced student - not yet an expert, but someone who has a good handle on the basics and is ready for more advanced training or beginning-level teaching.  It makes sense to think about it like a bachelors' degree in that sense - you've done real good, and now you're really ready to start learning from the best.

Higher rankings  or degrees (called *dans* in karate and judo, not sure about the rest) are used to signify greater advancement - in many styles, a new black belt may assist teaching classes, but may be teaching their own classes after reaching the 2nd or 3rd degree.  Many styles will call practitioners of around the 4th or 5th degree onward "masters" of the art, but that's not a hard and fast rule.  

Past a certain point, attaining a new degree tends not to be about passing a test, but is bestowed more as a sign of respect from the martial arts organization, in recognition of a master's achievements and dedication.  So at the upper levels (like 8th degree), there are usually going to be very, very few (if any) people holding that rank, and they're likely to be very old, very well-respected teachers.