What is the meaning of Index?

Most lenders tie ARM interest-rate changes to changes in an "Index rate." These indexes usually go up and down with the general movement of interest rates. If the index rate moves up, so does your mortgage rate in most circumstances, and you will probably have to make higher monthly payments. On the other hand, if the index rate goes down your monthly payment may go down. Lenders base ARM rates on a variety of indexes. Among the most common are the rates on one, three, or five-year Treasury securities. Another common index is the national or regional average cost of funds to savings and loan associations. A few lenders use their own cost of funds, over which, unlike other indexes, they have some control. You should ask what index will be used and how often it changes. Also ask how it has behaved in the past and where it is published.