Strong Nuclear Force; is the force that keeps the nucleons bound inside the nucleus of an atom. It is a short range attractive force that acts between all nucleons in the nucleus of the atom that is much stronger than electrical forces.
Binding energy; is the amount of energy needed to split the nucleus into individual protons and neutrons. It is the minimum energy required to separate a nucleus into free, unbound nucleons. The energy lost in the process of binding together the nucleons in the nucleus of an atom.
Mass defect is the difference between the mass of a nucleus and the sum of the masses of its component nucleons.