I just looked it up:
Predatory pricing (also known as destroyer pricing) is the practice of a firm selling a product at very low price with the intent of driving competitors out of the market, or create a barrier to entry into the market for potential new competitors. If the other firms cannot sustain equal or lower prices without losing money, they go out of business. The predatory pricer then has fewer competitors or even a monopoly, allowing it to raise prices above what the market would otherwise bear.
In many countries, including the United States, predatory pricing is considered anti-competitive and is illegal under antitrust laws. However, it is usually difficult to prove that a drop in prices is due to predatory pricing rather than normal competition, and predatory pricing claims are difficult to prove due to high legal hurdles designed to protect legitimate price competition.