A vertical stabilizer provides lateral stability to minimize yaw. The vertical stabilizer is sometimes referred to as the fin. There is a part of the airplane that extends along the top of the fuselage and connects to the vertical stabilizer. In some airplanes, like the Pilatus and Cessna 150 below
this part looks like it could have a substantial impact on yaw forces.
In other cases, like the Cherokee 140
it looks like it is mostly for inspecting the tail fin attachment.
My question is, “Does it have a name?”
In the Cessna 170 and Cessna 182 parts catalog, the part is much smaller, but it is called a “dorsal fin”. It is about the same size as a C152 on the C210 and has the same name. So at least for Cessna, the part is called a “dorsal fin”.
The PA-28 Cherokee manual just calls it a “Fairing – Fin”.