Plyometrics, or "plyos" for short, are a type of exercise designed to produce fast and powerful movements. They are generally used by athletes to improve performance in sports, especially those that involve speed, quickness and power. In addition, it is possible to find plyometrics used in the fitness field, but to a much lesser degree. Thus, plyometric exercises use explosive, fast-acting movements to develop muscular power and to improve overall speed. In other words, it's exercise that allows muscles to exert maximum force in the shortest amount of time possible.
Read more about Plyometrics: Introduction, History, Methodology: Plyometrics That Utilize The Shock Method, Plyometrics As Simple Jumping (with Little Regard For Time of Execution), Safety Considerations