Even a small amount of any substance contains very large number of atoms or molecules. Therefore, a quantitative adjective 'mole' is used to express the large number of sub-microscopic entities like atoms, molecules, ions, electrons, etc. present in a substance.
Thus, one mole is the amount of a substance that contains as many entities or particles as there are atoms in exactly 12 g (or 0.012 kg) of the carbon -12 isotope.
One mole is the amount of substance which contains 6.022\(\times 10^{23}\) particles/entities.
