Definition: a chemical mass unit, defined to be 6.022 x 1023 molecules, atoms, or some other unit. The mass of a mole is the gram formula mass of a substance.
Examples:
1 mole of NH3 has 6.022 x 1023 molecules and weighs about 17 grams. 1 mole of copper has 6.022 x 1023 atoms and weighs about 63.54 grams.
