The electronvolt (eV) is a unit of energy, but is not an SI unit. It is a commonly used unit of energy within physics, widely used in solid state, atomic, nuclear and particle physics, and high-energy astrophysics. It is commonly used with SI prefixes milli-(10), kilo-(10), mega-(10), giga-(10), tera-(10), peta-(10) or exa-(10). Giving meV, keV, MeV, GeV, TeV, PeV and EeV respectively. The SI unit of energy is the joule (J).