The term originated from the occasional black sheep which are born into a flock of white sheep due to a genetic process of recessive traits. Black wool was considered commercially undesirable because it could not be dyed. In 18th and 19th century England, the black color of the sheep was seen as the mark of the devil.
The transom is the flat back end of a boat. Some boats are pointed on both ends, so they have no transom. A traditional canoe, pointed on both ends has no transom. A modern square stern canoe (made to take an outboard motor) has a transom.
In naval architecture, a transom is the surface that forms the stern of a vessel. Transoms may be flat or curved and they may be vertical, raked forward, also known as a retroussÃ© or reverse transom, angling forward (toward the bow) from the waterline to the deck, or raked aft, often simply called raked, angling in the other direction.