What is amu?

ANSWER:

Atomic Mass Unit (amu):

“The unit used to express the relative atomic mass is called atomic mass unit (amu). It is 1/12th of the mass of one carbon atom.”

On C–12 scale, the relative atomic mass of ₆C¹² is 12.0000 amu and that of ₁H¹ is 1.008 amu.  

1 a.m.u. = 1.661×10^–27 kg

(Ref. An Insight Into Objective Chemsitry-11, Ch-01, Q. No. 15)