In the television series Terminator: The Sarah Connor Chronicles, "Heavy Metal" is a colloquial term or slang used by human characters, most notably Sarah and John Connor, to refer to Terminators. This designation highlights the machines' metallic endoskeletons and their formidable, unyielding nature.
The term serves as an informal, often derogatory, label for the relentless robotic assassins sent from the future to eliminate key figures or alter the timeline. It emphasizes their inorganic construction and their often destructive capabilities, distinguishing them from human beings. The use of "Heavy Metal" by the protagonists helps to create a sense of shared jargon and internal culture among those fighting against Skynet, providing a shorthand for their seemingly indestructible adversaries.