Mass defect

n. difference between the mass of an isotope and its mass number

Binding energy is the mechanical energy required to disassemble a whole into separate parts. A bound system has a lower potential energy than its constituent parts; this is what keeps the system together. The usual convention is that this corresponds to a positive binding energy.In general, binding energy represents the mechanical work which must be done in acting against the forces which hold an object together, while disassembling the object into component parts separated by sufficient distance that further separation requires negligible additional work.Electron binding energy is a measure of the energy required to free electrons from their atomic orbits.
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Noun
1. the amount by which the mass of an atomic nucleus is less than the sum of the masses of its constituent particles
(synonym) mass deficiency
(hypernym) mass

The quantity of mass which is converted into energy during, for instance, nuclear fusion or nuclear fission - and indeed in all nuclear, particle and chemical reactions too. Thus if a neutron and a proton undergo fusion to form a deuteron the mass of the deuteron is less than the sum of the constituents, this loss of mass appears as energy - a photon in this case. It is the binding energy of the deuteron, meaning that amount of energy must be provied to split deuterium back into a separate proton and neutron. The conversion takes place according to E=mc2, where m = mass defect and c is the speed of light.

Eng: mass defect
Urdu: فَرقِ کمیّت ۔ مَرکَزے کے کمیتی عدد اور اُس کے تَرکیبی ذَرّات کے عظیم تَر کُل کی کمیّت کے دَرمیان فَرق جو اُس توانائی کے برابر ہوتا ہے جو مَرکَزے کی تَشکیل سے خارَج ہوتی ہے ۔