Mogul skiing is a type of freestyle skiing

Freestyle skiing

Freestyle skiing is form of skiing which used to encompass two disciplines: aerials, and moguls. Except the two disciplines mentioned earlier Freestyle Skiing now consists of Skicross, Half Pipe and Slope Style...

 where skiers ski terrain characterized by a large number of different bumps, or moguls.
Moguls are a series of bumps on a trail formed when skiers push the snow into mounds or piles as they execute short-radius turns. They can also be constructed (seeded) on a slope for freestyle skiing

Freestyle skiing

Freestyle skiing is form of skiing which used to encompass two disciplines: aerials, and moguls. Except the two disciplines mentioned earlier Freestyle Skiing now consists of Skicross, Half Pipe and Slope Style...

 competitions or practice runs. Once formed, a naturally occurring mogul tends to grow as skiers follow similar paths around it, further deepening the surrounding grooves known as troughs.