Is there a difference between cardioversion and defibrillation?

Yes: Cardioversion encompasses defibrillation. Technically, if one is not in a fibrillating rhythm, the proper term for the act of delivering a shock to convert the rhythm back to normal is cardioversion, not defibrillation. In practice, the two terms are often used interchangeably however.

Not really: Technically yes, cardioversion is synchronized, defib is not.

Voltage: Cardioversion means using a stimulus to change the heart's beat from an abnormal rhythm to a normal one. Certain drugs can be used, or electricity, usually only a low voltage is required unless the abnormal rhythm is a very dangerous one called ventricular fibrillation. When the rhythm is ventricular fibrillation, usually more voltage (electricity) is needed, and it is called defibrillation.

Cardiovert: Cardioversion is the process of converting an abnormal cardiac rhythm to normal. It encompasses any means of doing that. Defibrillation is a subset of cardioversion. It is when a fibrillation rhythm, atrial or ventricular is converted to a more normal rhythm