Formula: Mass Defect Binding energy Mass difference Speed of light
$$W ~=~ \class{brown}{\Delta m} \, c^2$$
$$W ~=~ \class{brown}{\Delta m} \, c^2$$
$$\class{brown}{\Delta m} ~=~ \frac{W}{c^2}$$
Binding energy
$$ W $$ Unit $$ \mathrm{J} $$
Binding energy is the energy created from a part of the mass after individual nuclear constituents (protons, neutrons) have fused to form an atomic nucleus.
Mass difference
$$ \class{brown}{\Delta m} $$ Unit $$ \mathrm{kg} $$
A part of the mass of the protons and neutrons, which - during the fusion to a nucleus - was converted into the binding energy. The nucleus is lighter than the sum of its components!
Speed of light
$$ c $$ Unit $$ \frac{\mathrm m}{\mathrm s} $$
Speed of light is a physical constant and indicates how fast light travels in empty space (vacuum). It has the following exact value in vacuum:
$$ c ~=~ 299 \, 792 \, 458 \, \frac{ \mathrm{m} }{ \mathrm{s} } $$