What is 'hydroplaning' (aquaplaning) and how should an HTV driver respond to it?

1. When tires lose contact with the road and slide on a thin layer of water; the driver should release the accelerator and steer straight without braking hard
2. When the engine cooling system leaks water onto the road
3. A technique used to wash truck tires while driving
4. Accelerating hard to spray water away from the wheels