Avogadro's number, also known as NA, is 6.0221415 × 1023, and is the constant thing that links the world around us that we can see with the world around us that is submicroscopic -- the world we can't see. Avogadro's number represents the number of atoms in a mole, a standard unit of measurement used in chemistry.
But Avogadro didn't discover this number. The number was given his name as an honor because of an important discovery he made in the field of chemistry.
Lorenzo Romano Amedeo Carlo Avogadro was an Italian scientist living in the late 18th- to mid-19th centuries, during a time when scientists were discovering the basic ways atoms and molecules work. Avogadro's contribution was his theory -- Avogadro's Law -- that two gases that are equal volume, at the same temperature and at the same pressure, must each contain the same number of molecules regardless of the chemical nature of the gases.