Define the atomic mass unit?

Explanation

Atomic mass unit. In 1961 for a universally accepted atomic mass unit, carbon-12 isotope was chosen as the standard reference for measuring atomic masses. One atomic mass unit is defined as a mass unit equal to exactly one twelfth `(1//12^(th))` the mass of one atom of carbon-12.
The relative atomic masses of all elements have been found with respect to an atom of carbon-12.