The excess or deductible amount is the amount you are liable for in case of any damages to the vehicle. The amount could increase over and above the excess if the damages caused are excluded by the supplier's policy. So be sure to read the fine print!
A bond or security deposit is the amount the supplier will hold or authorise from your credit card. The most common way a rental company will collect this is to put a hold or "freeze" on the bond amount on your credit card.
Some rental companies will only take an imprint of your credit card and keep it on file until you bring back the vehicle undamaged.