GeV

A gigaelectronvolt (GeV) is a unit of energy equal to one billion ($10^9$) electronvolt. The mass of the proton and neutron is of the order of $1~\mathrm{GeV}/ c^2$.

Many energy-like quantities (masses, energies, momenta) of interest at the Large Hadron Collider are conveniently measured in GeV, using natural units.