Binding energy is sum of energy used to detach a particle from a particle system, or to release all of the system’s particles. For subatomic particles in atomic nuclei, for electrons bound to nuclei in atoms, and for atoms and ions bound together in crystals, binding energy is particularly important.
Nuclear binding energy is the energy needed to completely separate an atomic nucleus into its constituent protons and neutrons, or the energy that would be released by combining individual protons and neutrons into a single nucleus. The total mass of the bound particles is lower than the sum of the masses of the separate particles by an equivalent amount as expressed in the Einstein’s mass-energy equation with the binding energy..