In Italy millers grade their flour by using a 'zero' rating.
A single zero flour is quite coarse in texture, like very powdery semolina, whereas triple zero is much finer like cornstarch. But everyday flour is usually classed as double zero, or '00'.
The reason why 00 is internationally considered the best flour for making pasta and focaccia is that it's very finely ground, and two, it has a lower gluten content than most flours. Gluten, the natural protein that remains when starch is removed from wheat grains, creates the elasticity you feel when you bite into a crunchy slice of focaccia on on your favourite pasta shape.
Product of Italy.