A more thorough explanation:

Ex mora debitoris is a Latin term that means "on account of the debtor's delay." It is used in reference to a basis for charging interest on a debt.

For example, if a borrower fails to make a payment on time, the lender may charge interest on the outstanding balance ex mora debitoris.

Another example would be if a debtor takes longer than the agreed-upon time to pay back a loan, the lender may charge interest ex mora debitoris to compensate for the delay.

The examples illustrate how ex mora debitoris is used to justify charging interest on a debt when the debtor has delayed payment. It is a way for lenders to compensate for the extra time and risk involved in waiting for the borrower to fulfill their obligation.