Some cultures in the world have caste systems. A caste system is a socio-economic heirarchy, where a person is born into a position and sub-culture, whose worth is intrinsic and - theoretically - unvarying.
Caste Societies vary immensely. There can be few castes, many castes, many sub-castes within a few meta castes, religion-based castes, ethnicity-based castes, and other variants. Marriages and offspring outside of ones caste are possible in certain ways, but the prohibitions and the strength of these prohibitions vary from culture to culture.
Game groups from a non-caste society should probably not use a caste-bound native culture to work within. Caste-bound societies for these groups would probably work better as foreign cultures, unless they are loose castes lightly applied. People from modern western cultures have difficulty dealing with the limitations from castes. Groups are, of course, free to disregard this advice. You can, if you wish, use the following table, or construct one to your own tastes.
Roll Rigidity Base Complexity
1 Extreme Religion Byzantine
2 Very Rigid Religion Extraordinary
3 Rigid Ethnicity Hard to Understand
4 Moderately Rigid Ethnicity Complex
5 Moderate Religion and Ethnicity Layered
6 Somewhat Rigid Tribal Moderate
7 Somewhat Bendable Mixed Moderately Simple
8 Bendable Mixed Mostly Simple
9 Somewhat Fluid Mixed Simple
0 Fluid Mixed Trivial