A “sidecar” is:

1. A motorcycle with three wheels that are aligned one after the other.
2. A vehicle connected to the side of another vehicle with a bar that is not longer than 2.5 meters.
3. Correct answer: A fixture assembled on a wheel and connected to a motorcycle from the side, for the purpose of carrying a person or freight.
4. A vehicle driving next to another vehicle at the same speed.

WhyA sidecar is a fixture on its own wheel attached to the side of a motorcycle to carry a person or freight. Three wheels in a row or a car on a pole is not a sidecar.