They are expressions used in different parts of the world to mean the same thing - the first part of a claim that you are liable for if the vehicle is damaged or theft occurs. So if you hire a car with a £750 damage deductible, excess, super CDW or non waiver you will have to pay the car hire firm the first £750 of any damage caused to the car.
You can normally protect this excess with your car rental firm, although it is normally expensive - a guide price would be £10 - £15 a day. Car hire brokers will offer this insurance for around £5 - £7 per day but the most cost effective way is almost always by buying from insurers directly. Use MoneyMaxim to compare such policies which are priced from around £1.80 per day.