Answer:
Triangular trade usually evolves when a region has export commodities that are not required in the region from which its major imports come. Triangular trade thus provides a method for rectifying trade imbalances between the above regions.
For the British slave traders it was a three-legged journey called the 'triangular trade': West African slaves were exchanged for trade goods such as brandy and guns. Slaves were then taken via the 'Middle Passage' across the Atlantic for sale in the West Indies and North America.
So it got the name because of the three legged journey (A triangle had three ends)