In many martial arts, each practitioner's level is marked by the color of the belt. The Black Belt is often the highest belt color one can attain. The Red belt is also the rank of the great grand master. A red belt in Taekwondo is what a brown belt is in Karate. A red belt in Taekwondo signifies a student who is starting their year's study to become a black belt. It takes 1 year from earning the red belt to be eligible to test for the black belt. The red belt is earned at the rank 2nd Gup/Kup and it gains a black stripe at 1st Gup/Kup.
In other schools, a red belt signifies ninth or tenth degree Black Belt - tenth degree usually being the highest rank attainable. In Brazilian Jiu-Jitsu at the 9th degree, the black belt is replaced by an alternately red and black belt. The red belt is reserved for the art's founders (Hélio, Carlos,Carlson, etc.) and great grand masters and cannot be achieved through normal rank progression.
Many Kung Fu schools do not have a modern ranking system. Levels are measured in the course of years worked. Novice is 0 to 2 years, Intermediate is 2 to 4 years and Advanced is 4 years and beyond. The only belt (or sash) earned is the black. Everyone else wears a belt or sash representing the color of their school. Often this is a red belt or sash.