There are several terms used to describe the interest rates you pay on a mortgage, and the key terms are as follows:
Standard Variable Rate (SVR) - The SVR is the lenders standard rate. With a variable rate mortgage you are normally able to switch lenders at any time without being penalised. If you take out a mortgage that has a fixed, tracker or discounted rate once the set period of time ends the loan will usually revert to the Lenders SVR.
Fixed Rate - A fixed rate mortgage allows you to repay interest at a fixed rate, irrespective of any interest rate fluctuations. In other words your monthly repayments will remain the same every month for a time period agreed between you and your lender.
Tracker - A tracker mortgages usually tracks any movement in an index specified by the lender, this for example could be the Bank of England Base Rate for a set period, so you will benefit from any falls in interest rates, but will also have to pay more each month should the rate increase.
Discount - The discount mortgage rate is another variation of the standard variable rate. It provides a discount from the lenders SVR for a set period of time. The variable interest rate still fluctuates, meaning your monthly repayments may differ slightly from month to month, but the discount remains constant.