Avogadro is a fundamental concept in chemistry, named after the Italian scientist Amedeo Avogadro. He proposed that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules. This idea led to the understanding of the relationship between the amount of substance and the volume of gas. The number associated with Avogadro's hypothesis is known as Avogadro's number, approximately 6.022 x 10²³. This number represents the number of atoms, ions, or molecules in one mole of a substance, making it essential for calculations in chemistry and helping scientists quantify and compare different substances.