Debt is an obligation of repayment in the future. So technically it is money that we owe our future selves and others. Of course, the future is uncertain, which is what makes debt risky (and profitable). If we enter another recession, much of that debt could default.

This idea of basically seeing into the future, pricing risk/rewards was what always drew me to study finance. Sounds cool on paper, but the reality is much messier and morally ambiguous.