Short answers, pulled from the story.
The mole is the base unit for amount of substance in the International System of Units. It represents approximately 602 sextillion entities and allows chemists to bridge the gap between the microscopic world of individual atoms and the macroscopic world of laboratory measurements.
Wilhelm Ostwald coined the term mole in 1894, derived from the German word Molekül. The term did not appear in English textbooks until 1902, following decades of confusion between atomic mass and equivalent weight.
For most of the twentieth century, the mole was anchored to exactly 12 grams of carbon-12. This definition, adopted in the 1960s, created a direct numerical link between the mass of a substance in grams and its molecular mass in daltons.
The mole now contains exactly 6.02214076 times 10 to the power of 23 elementary entities. This change fixed the Avogadro constant as an exact number rather than a measured quantity subject to experimental error.
Mole Day is a holiday celebrated annually on the 23rd of October to honor the Avogadro number. The celebration runs from 6:02 a.m. to 6:02 p.m. to reflect the first three digits of the constant 6.02.