Bobtail
Definition

Bobtail refers to a truck operating without a trailer attached.

The word "bobtail" originates from the term bobbed, which traditionally means "shortened." It was first used to refer to animals, like horses or cats, that had their tails trimmed. In the context of trucks, "bobtail" describes a semi truck without a trailer, resulting in a "shortened" look. The absence of a trailer gives the truck a smaller appearance or one that seems "cut short," akin to the cropped tails of certain animals. This visual resemblance likely led to the adoption of the term.

When a driver doesn't have a trailer, it's called "bobtailing" in trucker slang. Usually, drivers don't like to go far without a trailer, as they tend to lose money.