Final answer:
In the context of interest rates, the extra amount which the lender adds to the index is called the margin.
Step-by-step explanation:
When a price, wage, or interest rate is adjusted automatically with inflation, economists use the term indexed. In the context of interest rates, the extra amount which the lender adds to the index is called the margin. The margin is a fixed percentage added to the index rate to determine the final interest rate for the borrower. For example, if the index rate is 3% and the lender's margin is 2%, the borrower's interest rate would be 5%.