Geek:
For level 6 and up you'll need at least 2 subclasses (specialized knowledge or experience) brought to level 4 to advance. So, you may have a concentration of experience with Comic books and Star Trek... once they have both achieved level 4 and you have enough experience to achieve level 6, you are officially a level 6 geek.
Level 6 = 64 experience + 2 subclasses at level 4 (each have 16 experience)
Level 7 = 128 experience + 2 subclasses at level 4
Level 8 = 256 experience + 2 subclasses at level 4
Level 9 = 512 experience + 2 subclasses at level 4
Levels 6 - 9 you are officially a certified geek. You probably have friends who share your interests and chat about things "normals" would not understand. You may have actually attended a convention or two.