A more thorough explanation:

A trade dollar is a type of United States dollar coin made of silver. It was issued from 1873 to 1878 for use in foreign trade, especially in eastern Asia. The purpose of the trade dollar was to compete with other countries' silver coins that were already in use in Asia.

Trade dollars were legal tender within the U.S. until 1876 when the coin's silver content fell to less than one dollar. After that, they were only used for trade purposes and not as regular currency.

For example, if an American merchant wanted to buy goods from China, they could use trade dollars instead of regular U.S. dollars. This made it easier for them to conduct business in Asia.

From 1878 to 1885, trade dollars were minted only in proof sets, which were special coins made for collectors. After 1885, they were discontinued altogether.

In summary, trade dollars were a type of silver coin used for foreign trade in the 19th century. They were legal tender in the U.S. for a short time and then used only for trade purposes. Today, they are valuable collectibles for coin enthusiasts.