A fraction was part of an entire number.
In 2365, while performing a comedy routine, Data said that "I come from a town so small, we had a fraction for a ZIP code." (TNG: "The Outrageous Okona")
Also that year, within the Dixon Hill series, the bartender Rex stated that he was "as jumpy as Haircut Lapinski trying to land on a fraction." (TNG: "Manhunt")