A measure of interest rate changes used to adjust the interest rate of an Adjustable Mrtgage Loan.

an index used to adjust the interest rate of an adjustable mortgage loan (e.g., the change in U.S. Treasury securities (T–Bills) with 1–year maturity. The weekly average yield on said securities, adjusted to a constant maturity of 1 year, which is the result of weekly sales, may be obtained weekly from the Federal Reserve Statistical Release H.15 (519). This change in interest rates is the "index" for the change in a specific Adjustable Mortgage Loan).

An index used to adjust the interest rate of an Adjustable Rate Mortgage (i.e.: COFI, LIBOR, 6 month T-Bill, etc.)