Question

what is 'amu' ? which quantity is measured in term of 'amu' ?

Answer 1

Amu is atomic mass unit ..it is defined as the quantity of mass exactly equal to 1/12th the mass of atom of carbon -12
atomic mass is measured in terms of amu

Answer 2

a.m.u ---> Atomic mass unit 

It can be also denoted as " u "

The atomic mass of an element is measured in terms of a.m.u ,  or  , u

For example :

The atomic mass of the element Oxygen is 16 u