What is the meaning of synchronized external cardioversion?

Cardioversion: When we shock ventricular fibrillation we just deliver the shock as soon as possible. When we cardiovert a rhythm like atrial fibrillation that kind of shock can cause ventricular fibrillation so we synchronize the shock to a safe part of the ECG complex. We call this synchronized cardioversion.

Shock : This is a procedure using patches placed on the skin over your heart. A synchronized "shock" is given at a particular time during the heart beat. The ideas to reset an abnormal heart rhythm, and regain normal rhythm.