The Japanese manufacture tractors for rice paddies. They are smaller than most U.S. tractors and perfect for a weekend farmer who wants to tend to a small garden. The tractors are not sold in the United States through any authorized channels, yet they are available in the U.S. at prices below the manufacturer's suggested retail price. What is the term for how these Japanese tractors are being sold?

Gray market refers to unauthorized marketing or trade. In business, the term gray (or grey) market is used to define the trading of goods and products that have been done unofficially, which means that has not been permitted officially. It may be legal but not official. It is also known as the over-the-counter market. In simple terms, when a good or product is sold without the permission of the brand owner, it is known as the grey market.

In the given case, the trading of Japanese tractors is unauthorized as they are sold without any authorized channels in the U.S. market.

Thus the correct answer is a grey market.