They are referring to the temporary loss of water weight in order to qualify for a weight class slightly below their usual wrestling weight. It gives them a strategic advantage if they go up against a person who is closer to the bottom of the weight class that is being targeted. The weight is usually lost by the use of a sweat suit during an aerobic workout.
What peter35 said, but, try not to put yourself in a position where dehydration is necessary to make weight. Get to that 4-5% body fat by healthy diet, and stop there. Next year you may want to start your diet 2-3 months before the season starts.