"Swooping" is when you come in to land at really high speed and pull back really hard so that you coast along, very close to the ground at high speed... can be upwards of 40 mph. The most dangerous variation of it is to swoop over water. If you touch the water, the drag will pull you in and then sometimes your parachute will land on top of you and drown you. Very exhilarating, but very dangerous. Most​ skydiving accidents are the result of bad decision making.

ETA: Hoser beat me to it.