Terms of the Trade: What is a Trunk Line?

a large, metal heating duct curving in a corner shape on the ceiling

Like the base of a tree that supports all its diverging branches, the trunk line of any system is the fundamental avenue through which the substance or service provided by any given utility flows.

In home design, this can refer to the main vent of a heating and cooling system, the fundamental water line, or the central cable of a telephone, cable, or internet connection.