Because heating value of fuels is described in many mass basis and thermodynamic conditions, the heating terms used in peer-reviewed literatures and reports have not been consistent. This short note aims to define and clarify the different uses of four most commonly used heating value terms, which are high heating value (HHV) or gross calorific value (GCV), low heating value (LHV), gross heating value (GHV) and net calorific value or net heating value (NCV or NHV), in the context of biomass fuels.