"caste", the word you are looking for is "caste". It's not just a difference in incomes, it's a closed system for reproduction (college educated often meet the

"caste", the word you are looking for is "caste". It's not just a difference in incomes, it's a closed system for reproduction (college educated often meet their future spouse in college, and even if not are rarely willing to marry non-college educated). Closed system for reproduction plus inheritance (genetic and cultural both) is the predecessor to castes, given a few more generations of this kind of separation.