A subprime mortgage, commonly called a junk mortgage, is a type of mortgage usually used for the purchase of housing, considered high risk because of the person to whom it is granted (borrower).
These are mortgages that have a high level of risk because they are granted to people who in normal conditions would not be eligible for one, either because they do not have a job or income or at least not in a stable manner.
In general, these mortgages are granted with an interest rate higher than the market rate, given the risk of non-payment involved.
Subprime mortgages became especially well known during the crisis that occurred in the USA in 2007, when many subprime mortgage customers could not meet their debts and the system could not withstand the pressure.
In 2007, in addition to the fact that the amount of subprime mortgages granted was much higher than recommended, they were granted for a higher value than the real value of the house that guaranteed their repayment.