A more thorough explanation:

A flexible-rate mortgage, also known as an adjustable-rate mortgage or a renegotiable-rate mortgage, is a type of mortgage in which the interest rate can be adjusted periodically based on changes in an external market index. This means that the borrower's monthly payments can increase or decrease over time.

For example, if a borrower takes out a flexible-rate mortgage with an initial interest rate of 3%, but the market index increases to 5%, the borrower's monthly payments will also increase to reflect the higher interest rate. Conversely, if the market index decreases to 2%, the borrower's monthly payments will decrease as well.

Flexible-rate mortgages can be beneficial for borrowers who expect their income to increase in the future, as they can take advantage of lower initial interest rates and potentially save money on monthly payments. However, they can also be risky for borrowers who are not prepared for potential increases in monthly payments.