Binding energy is a measure of the energy required to disassemble a physical system into its constituent parts. In nuclear physics, it refers to the energy that binds protons and neutrons together within an atomic nucleus; this energy is related to the difference between the total mass of the separate components and the actual mass of the assembled nucleus. Similarly, in atomic physics, the binding energy quantifies the energy holding an electron in orbit around a nucleus, a value dependent on the quantum state of the electron. More generally, the concept applies to chemical bonding, where the amount of energy released when atoms form chemical compounds defines the stability and strength of the resulting chemical bonds. The existence and quantification of binding energy are central concepts in understanding the stability and forces that govern matter at the subatomic level.