Mole

The mole is the legal (SI) unit of quantity of matter (symbol: mol). The contraction of "gram-molecule".
The quantity of matter in a system containing as many elementary entities as there are in 12g of carbon 12 atoms. (This number is called the Avogadro number = 6.022 x 10²³)
Example: one mole of dihydrogen molecules contains 6.022 x 10²³ molecules of dihydrogen.