What is a Trade Dollar Coin?

By GovMint :

The Trade Dollar was a U.S. coin minted from 1873 to 1885, designed to compete with other large silver trade coins in East Asia, particularly the Mexican Peso. The Trade Dollar was slightly heavier than the standard silver dollar, weighing 420 grains, and was primarily intended for export and use in trade abroad. The coin featured a design by William Barber, with a seated Liberty on the obverse and an eagle on the reverse.  Initially, Trade Dollars were legal tender in the U.S., but this status was revoked in 1876 due to their widespread circulation and devaluation. Despite this, production continued until 1878 for circulation and until 1883 for proof coins. The coins were demonetized in 1876 but were later re-monetized by the Coinage Act of 1965. 

Sources Used:

https://www.numismaticnews.net/collecting-101/the-strange-life-of-the-united-states-trade-dollar 

https://www.pcgs.com/coinfacts/category/trade-dollar-1873-1885/743