The retail value which is the higher of the two is the average price a dealer would sell the vehicle for taking its age, condition and mileage into account. If your vehicle is covered for its retail value, and it is either written-off, stolen or hijacked without being recovered, the settlement amount will be based on its retail value less the applicable excess. This will enable you to replace the vehicle with a similar model.
The market value is a lower than the retail value. A discounted premium is charged for clients selecting the market value.
Finally the trade or book value of the vehicle is the average price a dealer will pay you for your vehicle.
A good place to find out the value of your vehicle is on the TransUnionAuto web site.