Variable: displays all the variable rate mortgages including Standard Variable Rate (SVRs), Bank Base Rate (BBR), London Interbank Offer Rate (LIBOR), Stepped SVR, Capped, Tracker and Offset deals. These rates can change at any time.
Fixed Rate: you can fix your rate for a set period, typically for 2, 3, 4, 5 or 10 years, after which the mortgage usually reverts to a variable rate.
Discount Rate: the interest rate charged is lower for a fixed period after which time a higher rate is charged. This is usually on a variable rate.
Tracker: this is a variable rate that tracks a published interest rate (typically the London Interbank Offered Rate - known as LIBOR, or the Bank of England base rate plus a fixed interest rate amount on top), for example LIBOR plus 1.5%. Typically if the rate being tracked increases (e.g. the Bank of England base rate rise), so will your mortgage rate and hence your monthly payments will increase.
Capped Rate: this is a variable interest rate, but there is also a guarantee that the interest rate will not rise above a stated maximum.