The photographer has acknowledged a/his 'debt' to Andy Warhol. [=the photographer has said that his work was influenced by the photographs made by Andy Warhol]
banks with millions of dollars of 'bad debt' [=banks that have loaned millions of dollars that will not be repaid]
She's finally paid off her mortgage 'debt'. [=the money that she owed the bank to pay for her house]
(..) you invited me for a cup of coffee. Even though my wife is godmother to your only child. But let's be frank here. You never wanted my friendship. And you were afraid to be in my debt. I didn't want to get into trouble. I understand. You found Paradise in America. You made a good living, had police (..)1972 The Godfather