Electrocution or electric shock is when electricity passes through something living. It happens when the human body gets in contact with electric current. The word "electrocution" originally meant execution on electric chair, but can mean today any accident with electricity.
The human body can stand voltage well, but not very much electric current. If the electric current is strong, it can stop heartbeat and cause death. Very high voltage and/or current can cause severe burns and even fry the victim alive.