Upvote:5
I can't answer when the term was first used but I can take a guess on why it was called that.
Arab sailors sailing the spice routes would have been dependent on the winds. Crossing the Indian Ocean, they would have experienced the prevailing winds, known as trade winds, blowing from the North East. So from the point of view of these Arab sailors, "the world east of the Bay of Bengal" would have been "behind the wind".