When the center of an atom is formed, it weighs less than the total weight of its individual parts; what is the specific term for this missing amount of mass?

The specific term for this missing amount of mass when the center of an atom, called the nucleus, is formed is mass defect. Mass defect is the difference between the total mass of the individual, unbound nucleons (protons and neutrons) that make up a nucleus and the actual measured mass of that nucleus. Protons are subatomic particles with a positive charge, and neutrons are subatomic particles with no charge; both are found in the nucleus and are collectively referred to as nucleons. This mass is not truly 'missing' but is converted into a tremendous amount of energy according to Albert Einstein's mass-energy equivalence principle, famously expressed by the equation E=mc². Here, E represents energy, m represents mass, and c is the speed of light. The energy released during the formation of the nucleus from its constituent nucleons, corresponding to this mass defect, is known as the nuclear binding energy. Nuclear binding energy is the energy required to disassemble a nucleus into its individual protons and neutrons, or conversely, the energy released when those nucleons combine to form the nucleus. This release of energy makes the nucleus more stable than its separated parts. The greater the mass defect, the greater the nuclear binding energy, indicating a more stable nucleus.