What is a tractor-trailer commonly referred to as?

A tractor-trailer is commonly referred to as a semi truck because it consists of a tractor unit that provides the power and a trailer that carries the cargo. The term "semi" comes from the fact that the trailer is not a standalone vehicle; it relies on the tractor for mobility. This configuration allows for greater hauling capacity and flexibility in transporting various types of cargo compared to other vehicles.

While pickup trucks, box trucks, and flatbed trucks are all types of vehicles used for transportation, they do not have the same design or capabilities as a tractor-trailer. Pickup trucks are generally smaller and suited for lighter loads, box trucks are enclosed and usually used for local deliveries, and flatbed trucks lack a trailer with sides and a roof, making them more suitable for specific types of cargo. Understanding these distinctions helps clarify why the term "semi truck" accurately describes a tractor-trailer.