A mole (abbreviation: mol) is an amount of substance that contains as many objects (molecules, particles, ions, cells etc.) as the number of atoms in exactly 12 grams of 12C (carbon). This number can be determined experimentally to be 6.022 x 1023 (602,200,000,000,000,000,000,000), a number which is called Avogadro's number. The mole is simply a convenient unit for dealing with large numbers just like it is easier to talk about the weight of a ship in tons rather than ounces. Mole has several other possible meanings, of course, but none of these generally applies to material safety data sheets.
