A **tram** is not considered a motor vehicle, despite having a motor, due to its special characteristics. Trams are vehicles that run on rails and are designed for passenger transport in urban areas. This particularity excludes them from the category of motor vehicles, which generally includes those that need a motor to operate and do not depend on rails.

On the other hand, a **truck** and a **motorcycle** are considered motor vehicles. Trucks are automobiles designed to transport goods and require a motor to function. Motorcycles, whether two-wheeled or with a sidecar, are also automobiles that need a motor to move.

In summary, the tram is the only one of the three that is not classified as a motor vehicle due to its operation on rails and its specific use in urban transport.