A "triangular trade" is any three-way exchange, but the term is often used to refer to one particular instance: the 18th century trade between Europe, the west coast of Africa, and the Caribbean.
Ships from Europe would ply the African coast purchasing slaves from and sell them in the Caribbean (typically for on-sale to the United States) before sailing back to Europe with agricultural products such as sugar and cocoa. This makes a triangle on a map hence the term "triangular trade."
The triangular trade involved three principal commodities: sugar, rum, and slaves. European distillers made rum from Caribbean sugar. European slave ships took vats of the rum to Africa and bought African slaves from their African owners with the rum. The bulk of the human cargo was sold in the Caribbean in trade for cane sugar. The sugar was then taken back to Europe, and the cycle continued. At each stop along the way, an excellent profit was made.
Surplus slaves not sold in the Caribbean or Latin America were brought on Europe an ships in the triangular trade to the American South and sold to the large plantations. Cotton in the American South was sold primarily to English textile mills which became the basis for industrialization in England and the subsequent British Empire.
