With a fixed rate loan your interest rate and repayments are fixed for a set period, usually between one and five years. The major benefit with fixed rate loans is that you know exactly what the repayments are for that period of time, regardless of what the market does.
Most fixed loans will automatically default to a variable loan at the end of the term, but can rollover to another fixed term at the rate of the day. The rate is usually the interest rate at the time settlement, not at the time of application. A `rate lock' facility is available through most lenders, but this usually attracts a fee.