The difference between the total mass of individual nucleons (i.e. total number of proton and neutron) and actual mass of nucleus of that energy is called binding energy.$\Delta m = \left (P \times m_{P} + N \times m_{N} \right) - m_{actual} \qquad (1)$
$\Delta m \rightarrow$ Mass Defect
$P \rightarrow$ Number of Proton
$N \rightarrow$ Number of Neutron
$m_{actual} \rightarrow$ Actual mass of nucleus
$m_{P} \rightarrow$ Mass of a Proton
$m_{N} \rightarrow$ Mass of a Neutron
$Z \rightarrow $ Atomic Number
$A \rightarrow $ Atomic Mass Number
$ e \rightarrow $ Number of Electrons
The energy require to form or break a nucleous is called the binding energy of nucleous.$B.E= \Delta m \times c^{2} Joule$
The energy require to emit one nucleon from the nucleous is called binding energy per nucleon.$B.E. \: per \: nucleon = \frac{B.E.}{ Total \: No. \: of \: Nucleons}$