When an automobile is driven fast on wet roads, especially if it has worn-out tires, a cushion of water can build up under the tires, preventing the rubber from contacting the road. This is very scary and dangerous, because it leads to a total loss of traction.
Fortunately for cyclists, this cannot happen to a bicycle; they don't go fast enough, nor have a large enough contact patch, nor do the tires run at a low enough pressure to make hydroplaning possible.
Even with automobiles, actual hydroplaning is very rare. It is a much more real problem for aircraft landing on wet runways. The aviation industry has studied this problem very carefully, and has come up with a general guideline as to when hydroplaning is a risk.
An ill-founded fear of hydroplaning often leads people to buy bicycle tires with inefficient tread patterns, when they would be better off with slicks.
Tread patterns on road tires are purely cosmetic, and have no practical value on hard, paved surfaces.