What is meant by mole and molecular mass

The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.022 140 76 × 10²³ elementary entities. This number is the fixed numerical value of the Avogadro constant, N_A, Any group with Avogadro number quantities is called a mole.

Molecular mass or molecular weightis the mass of a molecule. It is calculated as the sum of the atomic weights of each constituent element multiplied by the number of atoms of that element in the molecular formula
eg: molecular mass of O2 is 2×16 = 32