The word "kyu" refers to "student". There are ten "kyu" or student grades prior to attaining a "dan" grade which is the first level of the black belt grades. Kyokushin uses a ten belt kyu rank system shown below. Kyu ranking students are also referred to as "mudansha"; without "dan" grade.
white belt (no rank)
orange belt with blue stripe
blue belt with yellow stripe
yellow belt with green stripe
green belt with brown stripe
brown belt with black stripe
After completing the kyu ranks, the student then moves into the "dan" / black belt levels. The first degree black belt level is called "shodan". "Sho" means beginner. Therefore, the student is now considered a "yudansha" and begins anew at the first level of the more advanced dan grades.
There is both an adult (ages 13 and up) and a children's (ages 5 - 12) training syllabus. Students should refer to the syllabus on a regular basis to ensure that their training efforts are aligned with the requirements for their particular rank.