What is "dumping" as noted in the biography, Factory Man?

John Bassett was determined to fight off the “Chinese invasion” and keep his factory doors open and his work force employed. John headed a petition to the U.S. Commerce Department to investigate Chinese furniture makers that he claimed using cut-throat practices that harmed domestic furniture makers. This practice was referred to as underselling or “dumping” and John was seeking an “antidumping” case against the Chinese manufacturers which, if successful, would result in heavy duties being levied against them.