Heavy rail: Meaning (information, definition, explanation, facts)

The term heavy rail is often used for regular railways, to distinguish from systems such as trams/light rail and metro. However, in the U.S.A. the term is used as the general term for metro systems: underground systems and systems that are not running below the ground but are similar to underground systems in other respects; when the term is used in this way, it should be distinguished from commuter rail and inter-city rail services, which cover longer distances.