energy density

Energy density is the amount of energy stored in a given (unit) volume, e.g., J/m³ (joules per meter cubed). The concept is used in engineering (often for the density of the energy available for extraction from something, such as a type of battery) and science, including astrophysics. One use is in radiative transfer models, using density of energy of the electromagnetic radiation passing through a volume at a given time as a term in formulas. Another use is to characterize the energy inherent in magnetic fields.