Fixed rate mortgages are the 'classic' style. With these, your repayments are fixed and will not change no matter what happens to the financial climate.
Some lenders may offer fixed rate mortgages over a certain number of years and then switch to a standard variable rate mortgage. Often there will be a penalty for overpayments or to end the mortgage early.
A fixed rate mortgage is good if you need to budget for a given period of time, as you can shop around for the best introductory offer and still take advantage of variable rate mortgages a few years down the line.
