Fractional stops
From The Glossary of Digital Photography
Refers to f-stops located in between the whole stops. Digital cameras will allow for usually one-third or even one-eighth stops. Some examples of one-third stops are f/ 2.8, f /3.2, f /3.5, f /4, f/ 4.5, f /5, f /5.6, f /6.3, f /7.1, and f /8. The whole stops are shown in bold; the one-third stops are the two stops in between the whole stops.
