What is the phenomenon known as 'hydroplaning' (aquaplanage) and what should a driver do if it occurs?

1. Tyres lose direct contact with the road surface due to a layer of water; ease off the accelerator and keep the steering wheel straight without harsh braking
2. Water enters the engine cylinders; slam on the brakes immediately and turn the wheel sharply
3. Brakes lock completely due to air in the lines; pull the handbrake immediately
4. Tyres deflate due to water pressure; accelerate to regain traction