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.
And what does the different heights of a transom matter? I was looking up boats on websites for the companies and they had transom heights for the boats, what does that mean? The transom is the top sides of the stern of the boat. It may be perpendicular or angled forward or aft. Many boats have an inboard engine, so no outboard to mount, yet the boat still needs a transom. The stern is the aft section of the boat, the transom is the surface that forms the stern of the vessel. Some transoms can even be round or pointed as in a canoe stern.