What is 'aquaplaning' (or hydroplaning) and how should you control it?

1. When tyres lose all contact with the road and slide on a thin film of water; release the accelerator and steer straight
2. When the engine overheats due to rain water entering the radiator; stop the vehicle
3. When brakes fail completely in wet weather; pump the brakes quickly
4. When the vehicle's electrical system shorts out in heavy rain; restart the engine