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Hampton Roads Transit, the mass transit system for the Hampton Roads, Virginia area

Hartwell Railroad Company

Heart rate turbulence, the return to equilibrium of heart rate after a premature ventricular contraction (PVC)

High rising terminal, a feature of speech

Holden Racing Team, a V8 Supercar racing team

Hormone replacement therapy, a system of medical treatment for perimenopausal and postmenopausal women

Hormone replacement therapy (trans), for transgender people

Hostage Rescue Team, of the US Federal Bureau of Investigation

Hrvatska radiotelevizija (Croatian Radiotelevision), the Croatian public broadcasting corporation

Humane Research Trust, a British medical research charity

RAF Linton-on-Ouse, the IATA airport code