what does scout mean by there was a "caste" system in maycomb?

A caste system is any system in which people are divided in some way, most often by ethnic, racial, or financial lines. In Maycomb, there is the obvious white upper class, represented by Atticus and his friends and family; there are the poor black citizens represented by the citizens such as Tom Robinson; there are the "other white citizens" who, for example, make up the jury; there are the poor white "trash" represented by Robinson's accuser and her family. These people represent different ways of living and indeed a different place in the social order.

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"There was indeed a caste system in Maycomb, but to my mind it worked this way: the older citizens, the present generation of people who had lived side by side for years and years, were utterly predictable to one another: they took for granted attitudes, character shadings, even gestures, as having been repeated in each generation and refined by time. Thus the dicta No Crawford Minds His Own Business, Every Third Merriweather Is Morbid, The Truth Is Not in the Delafields, All the Bufords Walk Like That, were simply guides to daily living: never take a check from a Delafield without a discreet call to the bank; Miss Maudie Atkinson’s shoulder stoops because she was a Buford; if Mrs. Grace Merriweather sips gin out of Lydia E. Pinkham bottles it’s nothing unusual—her mother did the same."

A caste system is any system in which people are divided in some way, most often by ethnic, racial, or financial lines. In Maycomb, there is the obvious white upper class, represented by Atticus and his friends and family; there are the poor black citizens represented by the citizens such as Tom Robinson; there are the "other white citizens" who, for example, make up the jury; there are the poor white "trash" represented by Robinson's accuser and her family. These people represent different ways of living and indeed a different place in the social order.

"There was indeed a caste system in Maycomb, but to my mind it worked this way: the older citizens, the present generation of people who had lived side by side for years and years, were utterly predictable to one another: they took for granted attitudes, character shadings, even gestures, as having been repeated in each generation and refined by time. Thus the dicta No Crawford Minds His Own Business, Every Third Merriweather Is Morbid, The Truth Is Not in the Delafields, All the Bufords Walk Like That, were simply guides to daily living: never take a check from a Delafield without a discreet call to the bank; Miss Maudie Atkinson’s shoulder stoops because she was a Buford; if Mrs. Grace Merriweather sips gin out of Lydia E. Pinkham bottles it’s nothing unusual—her mother did the same."