"TDR" is Troubled Debt Restructuring. This means that the lender renegotiated the terms of a loan and the rate is now below the market average; the lender gave up interest, or reduced the principal owed, as typical examples. This would be done when the borrower could not meet the terms of the original agreement, but the bank believes these new terms will lead to a repaid debt.
This renegotiation of the debt could mean that all or some of the collateral securing the loan was sold or turned over to the lender. In this case, it may be considered a settled debt when that collateral is valued at equal to or more than the debt owed. As for "STDR", it may be that the "S" is for "settled" meaning the borrower gets to walk away.
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